Furnace  Efficiency 

Combustion  and  Flue  Gases 


BY 

JAMES  C.  PEEBLES,  M.  M.  E. 


CHICAGO 

THE  JOSEPH  G.  BRANCH  PUBLISHING  CO. 
1914. 


COPYRIGHT,    1014 

by 
JOSEPH   G.    BRANCH 


PREFACE 

Coal  is  the  great  source  of  energy  from  which  is  de- 
rived by  far  the  greatest  part  of  the  mechanical  and 
electrical  power  now  used  in  the  industrial  world.  From 
the  beginning  of  civilization  man  has  made  use  of  this 
great  source  of  energy  apparently  with  the  idea  that  i- 
is  an  inexhuastible  supply.  But  unfortunately  the  coal 
supply  is  not  unlimited  and  the  time  must  come  when  it 
will  be  exhausted.  What  we  will  do  for  power  when 
that  time  arrives  is  a  problem  for  future  generations  to 
solve. 

The  problem  for  the  present,  generation  to  consider  is 
the  economical  use  of  our  available  coal  supply,  so  that 
the  time  when  the  coal  will  be  exhausted  may  be  post- 
poned as  long*  as  possible.  There  is  perhaps  no  class  of 
men  so  intimately  in  touch  with  the  problem  of  the  con- 
servation of  our  coal  supply  as  the  operators  of  steam 
power  plants.  A  vast  amount  of  coal  is  consumed  every 
year  in  the  power  plants  of  the  world  and  power  plant 
operators  should  be  able  to  do  much  towards  the  solu- 
tion of  this  important  problem. 

It  is  the  chief  engineer,  the  man  in  responsible  charge 
of  the  power  plant,  to  whom  we  must  look  for  economy 
in  the  use  of  fuel.  He  should  be  familiar  with  the 
latest  and  best  work  that  has  'been  done  on  the  problem 
of  combustion,  and  should  instruct  his  firemen  and  others 
in  his  plant  how  to  operate  the  furnaces  at  highest 
economy. 

The  purpose  of  the  author  in  preparing  this  -book  has 
been  to  set  forth  in  convenient  form  and  in  as  non-tech  - 
nical  language  as  possible  the  efforts  that  are  now  being 
marie  to  increase  the  efficiencv  of  coal  combustion  in  the 


341821 


FURNACE  EFFICIENCY 

steam  boiler  furnace.  It  should  be  of  special  interest  to 
all  chief  engineers  of  steam  power  plants,  but  it  is  be- 
lieved that  every  man  having  anything  to  do  with  the 
power  plant,  from  manager  or  superintendent  to  fireman, 
will  'find  something  of  interest  and  value  in  its  pages. 

Competition  in  all  lines  O'f  business  has  now  become  so 
keen  that  all  waste  and  inefficiency  must  be  reduced  to 
the  absolute  minimum.  The  power  plant  operator  can 
no  longer  waste  fuel  without  being  called  to  account,  and 
hence  the  chief  engineer  must  keep  up  with  the  times  in 
matters  of  combustion  or  he  may  find  himself  displaced 
by  a  more  up-to-date  man.  It  is  believed  that  this  book 
wijl  make  clear  to  the  engineer  how  he  can  operate  his 
particular  plant  at  maximum  efficiency  as  regards  the 
boiler  room. 

The  thanks  of  the  author  are  hereby  extended  to  the 
various  manufacturers  of  furnace  equipment  who  have 
very  .kindly  supplied"  many  of  the  illustrations  used.  He 
is  particularly  indebted  to  tllfc  engineers  of  the  Green 
Engineering  Company  for  many  helpful  suggestions. 
Obligation  must  also  be  acknowledged  to  Air.  Joseph 
W.  Hays  and  Mr.  Joseph  G.  Branch,  to  the  writings  of 
the  former  for  certain  data  and  illustrations,  and  to  the 
latter  for  many  helpful  criticisms  and  suggestions. 

THE  AUTHOR. 
Chicago,  May,  1914. 


TABLE  OF  CONTENTS 

CHAPTER  I. 
Chemistry  of  Combustion 1 

CHAPTER  II. 
Flue-Gas  Analysis 10 

CHAPTER  III. 
Reduction  of  Losses  in  the  Boiler  Furnace 21 

CHAPTER  IV. 
Draft  Losses  in  Furnace  and  Boiler 29 

CHAPTER  V. 
Smoke  and  Its  Prevention -40 

CHAPTER  VI. 
Smokeless  Furnaces 51 

CHAPTER  VII. 
Wilsey  Fuel  Economy  Gauge.. 64 

CHAPTER  VIII. 
Blonck  Efficiency  Meter 75 

CHAPTER  IX. 
The  Chain-Grate  Stoker 90 

CHAPTER  X. 
The  Murphy  Furnace 106 

CHAPTER  XI. 
The  Jones  LTnder-Feed   Stoker 119 

CHAPTER  XII. 
Arches,  Breeching,  and  Smoke-Stack 131 

CHAPTER  XIII. 
Breeching   and   Chimney 140 


Furnace  Efficiency 


CHAPTER  I. 

In  practically  all  steam-power  plants  the  largest 
single  item  of  operating  expense  is  the  coal  bill.  If 
we  wish  to  run  the  plant  economically  it  would  seem 
to  be  reasonable  to  try  to  save  money  where  we  spend 
the  most  of  it.  But  the  history  of  operating  engineer- 
ing practice  in  the  steam  plant  shows  that  this  has  not 
been  the  case,  at  least  not  until  very  recently.  The 
engineer  will  spend  much  time  and  thought  on  his 
engine,  putting  it  in  the  best  possible  condition  for 
efficient  operation;  this  is  perfectly  proper  and  is  a 
mark  of  the  progressive  engineer.  Too  often,  how- 
ever, his  efforts  at  increased  efficiency  and  economy 
stop  with  the  engine,  in  spite  of  the  fact  that  in  the 
average  plant  dollars  can  be  saved  in  the  furnace  room 
where  dimes  are  saved  at  the  engine. 

It  has  been  said  that  necessity  is  the  mother  of 
invention,  and  it  is  equally  true  that  competition  is  the 
mother  of  economy  and  efficiency.  The  operating 
engineer  is  just  beginning  to  feel  the  competition  of 
the  big  power  and  light  companies,  and  that  competi- 
tion is  going  to  become  keener  as  time  goes  on.  It  is 
no  exaggeration  to  say  that  the  central-station  solici- 
tor is  after  the  engineer's  job,  and  he  will  get  it  if  he 
:an  show  the  boss  that  the  big  company  will  furnish 
him  with  power  cheaper  than  he  can  generate  it  in 
his  own  plant.  On  the  other  hand,  if  the  operating 
engineer  is  progressive  and  up  to  the  minute  on  all 


2  FURNACE  EFFICIENCY 

points  affecting  economy  and  efficiency  of  operation, 
in  most  cases  he  will  be  able  to  show  the  power-plant 
owner  a  set  of  figures  on  power  cost  which  the  cen- 
tral-station man  is  unable  to  meet.  It's  all  a  question 
of  the  most  power  for  the  least  money,  and  unless  the 
operating  engineer  in  the  small  plant  can  generate 
power  for  a  little  less  money  than  the  central  station 
will  supply  it,  his  plant  will  be  shut  down  and  he  will 
be  out  of  a  job. 

It  is  our  purpose  here  to  discuss  some  of  the  prob- 
lems which  arise  in  the  furnace  room  and  which  are 
vital  to  the  economical  operation  of  the  plant.  In  the 
past  too  little  attention  has  been  given  to  furnace 
operation,  with  the  result  that  in  the  average  plant 
large  fuel  waste  has  become  the  rule  rather  than  the 
exception.  The  statement  that  the  majority  of  steam 
plants  waste  10  per  cent  of  the  coal  used  is  probably 
not  far  from  the  truth,  while  many  "  terrible  exam- 
ples "  exist  where  as  much  as  40  per  cent  of  the  fuel 
is  wasted.  Wouldn't  it  be  worth  while  to  reduce  your 
coal  bill  10  per  cent  or  more?  It  would  make  you 
"  solid  "  with  the  boss,  and  the  central-station  solicitor 
wouldn't  call  the  second  time. 

The  function  of  a  boiler  furnace  is  to  transform  the 
heat  energy  of  the  coal  into  a  form  available  to  the 
boiler,  and  to  deliver  it  in  that  form  with  the  least 
possible  loss.  The  function  of  the  boiler  is  to  use  this 
energy  in  the  generation  of  steam.  Thus  the  furnace 
and  the  boiler  have  different  functions  to  perform,  and 
in  all  of  our  efforts  toward  economy  of  operation  we 
must  recognize  this  fact.  The  efficiency  of  the  furnace 
is  perhaps  more  influenced  by  the  manner  of  its  han- 
dling than  is  the  case  with  the  boiler,  and  for  that 
reason  the  furnace  offers  the  more  fruitful  field  for 
effort  toward  greater  efficiency  through  increased  care 
in  operation.  We  shall  therefore  devote  the  greater 
part  of  our  attention  to  the  furnace. 


FURNACE  EFFICIENCY  3 

In  the  first  place,  if  we  wish  to  improve  furnace 
efficiency  and  so  get  more  steam  with  less  coal,  we 
must  have  some  standard  by  which  to  judge  the  fur- 
nace. In  other  words,  we  must  be  able  to  recognize 
an  efficient  furnace  when  we  see  it.  Most  engineers 
would  say  that  an  evaporative  test  is  the  best  guide 
to  furnace  efficiency,  but  this  is  not  the  case,  because 
the  evaporative  test  depends  upon  both  boiler  and 
furnace  and  is  the  measure  of  their  combined  effi- 
ciency, while  for  the  present,  at  least,  we  are  inter- 
ested only  in  the  furnace.  A  boiler  in  bad  condition, 
covered  with  soot  and  lined  on  the  inside  with  scale, 
might  give  a  low  evaporation  even  when  furnace  effi- 
ciency was  reasonably  good.  Thus  the  evaporative 
test  is  not  the  rule  by  which  to  measure  furnace  effi- 
ciency. 

One  prominent  engineer  has  defined  an  efficient 
boiler  furnace  as  one  which  completely  consumes  the 
combustible  in  the  fuel  with  least  possible  excess  of 
air.  This  is  the  proper  test  to  apply  to  the  furnace, 
and  the  only  one  which  tells  us  all  we  need  to  know 
about  it.  It  is  not  our  purpose  in  this  connection  to 
enter  into  a  discussion  of  the  theory  of  the  combus- 
tion process.  A  knowledge  of  the  chemistry  of  com- 
bustion may  be  desirable  from  an  academic  point  of 
view,  but  it  doesn't  require  a  chemist  to  operate  a 
boiler  furnace  efficiently  any  more  than  it  requires 
an  expert  in  thermodynamics  to  run  a  steam  engine. 

The  important  question  is :  Are  we  burning  all  the 
combustible  in  the  fuel  with  just  as  small  an  excess 
of  air  as  possible?  To  answer  this  question  we  must 
be  able  to  analyze  the  gases  of  combustion  coming 
from  the  furnace.  The  practical  engineer  should  not 
become  discouraged  at  the  use  of  the  word  "  analyze." 
There  is  nothing  about  boiler-flue-gas  analysis  which 
any  engineer  can  not  understand ;  in  fact,  he  can  even 
instruct  his  fireman  how  to  make  the  analyses. 


4  FURNACE  EFFICIENCY 

Every  engineer  knows  that  the  chief  combustible 
part  of  coal  is  carbon.  The  burning  of  coal  in  the 
furnace  is  practically  nothing  more  than  the  combin- 
ing of  this  carbon  with  the  oxygen  of  the  air.  Air  is 
only  about  21  per  cent  oxygen,  the  remaining  79  per 
cent  being  mostly  nitrogen,  which  takes  no  part  in  the 
burning.  The  function  of  the  nitrogen  in  the  air  is 
merely  to  dilute  the  oxygen.  When  carbon  unites 
with  oxygen  it  forms  a  gas,  called  carbon  dioxid,  rep- 
resented by  the  symbol  CO2,  which  means  one  part 
of  carbon  and  two  parts  of  oxygen.  This  carbon 
dioxid  will  therefore  be  present  in  the  gases  coming 
from  the  furnace,  and  it  is  the  amount  of  this  CO2 
in  which  we  are  chiefly  interested  in  the  flue-gas 
analysis. 

If  all  the  21  per  cent  of  oxygen  which  the  air  con- 
tains were  to  be  consumed  in  the  furnace  and  turned 
into  CO2,  then  the  products  of  combustion  coming 
from  the  fire  would  contain  just  21  per  cent  of  this  gas. 
That  is,  if  just  the  proper  amount  of  air  were  supplied 
and  if  all  the  combustible  in  the  coal  were  consumed, 
the  flue  gases  would  contain  21  per  cent  of  CO2.  But 
in  actual  practice  it  is  never  possible  to  realize  this 
ideal  condition,  due  chiefly  to  the  fact  that  the  oxygen 
of  the  air  can  not  be  brought  into  close  enough  con- 
tact with  all  of  the  combustible  of  the  fuel  to  produce 
complete  combustion  unless  there  is  some  extra  air 
present.  The  result  is  that  in  all  boiler-furnace  prac- 
tice an  excess  of  air  is  always  allowed  to  pass  into 
the  furnace,  so  as  to  make  sure  that  all  of  the  com- 
bustible in  "the  fuel  will  be  burned.  An  excess  of 
40  per  cent  to  50  per  cent  represents  good  practice, 
but  many  times  it  runs  up  to  100  per  cent,  200  per 
cent,  and  even  higher.  Suppose  that  100  per  cent 
excess  air  is  being  used ;  this  means  that  just  twice 
as  much  air  is  passing  into  the  furnace  as  is  needed 
under  ideal  conditions  to  completely  burn  the  fuel. 


FURNACE  EFFICIENCY  5 

Under  these  conditions  the  gases  coming  from  the 
furnace  will  contain  only  half  as  much  CO2  as  before, 
because  one-half  of  the  air  is  passing  through  the 
furnace  unchanged.  That  is,  the  CO2  will  now  be 
only  Wy2  per  cent  instead  of  21  per  cent.  Joseph  W. 
Hays,  a  well-known  expert  on  combustion  engineer- 
ing, illustrates  this  point  as  follows :  Suppose  that  a 
quart  of  milk  contains  21  per  cent  of  cream;  now  if 
\ve  add  one  quart  of  water  to  the  milk  we  shall  have 
no  more  cream  than  before,  but  we  shall  have  two 
quarts  of  "  near  "  milk.  Therefore,  the  cream  is  now 
only  I0y2  per  cent  of  the  whole,  or  just  one-half  of 
what  it  was  before. 

The  point  that  must  be  clearly  understood  here  is 
that  the  percentage  of  CO2  in  the  flue  gases  is  a  direct 
index  of  the  amount  of  excess  air  which  is  passing 
through  the  furnace.  Suppose  that  the  flue  gas  shows 
7  per  cent  CO2;  the  percentage  of  excess  air  under 
these  conditions  may  be  calculated  as  follows: 

21  ~7   X  100  ==  200  per  cent  excess. 

Subtract  the  observed  percentage  of  CO2  from  21 ; 
divide  this  remainder  by  the  percentage  of  CO2 ;  mul- 
tiply this  result  by  100.  Thus  the  flue  gas  analysis 
provides  a  convenient  method  for  measuring  the  effi- 
ciency of  the  furnace,  because,  as  we  have  seen,  the 
efficient  furnace  is  one  which  consumes  the  com- 
bustible in  the  fuel  with  the  least  possible  excess 
of  air. 

Let  us  examine  this  definition  of  an  efficient  fur- 
nace and  see,  if  possible,  why  excess  air  reduces  fur- 
nace efficiency.  A  brief  study  of  the  chemistry  of 
the  combustion  process  shows  that  it  requires  about 
10>^  pounds  of  air  to  burn  1  pound  of  coal.  Of  course, 
this  differs  somewhat  with  different  coals,  but 


6  FURNACE  EFFICIENCY 

pounds  is  a  fair  average  figure.  If  in  addition  we  allow 
for  an  excess  of,  say,  50  per  cent,  there  will  be  15^4 
pounds  of  air  passing  through  the  furnace  for  every 
pound  of  coal  thrown  onto  the  grate.  This  excess  air, 
5^4  pounds  per  pound  of  fuel,  passes  through  the  fur- 
nace and  up  the  smokestack  unchanged,  except  in 
one  important  particular.  Its  temperature  has  been 
raised.  The  average  yearly  temperature  of  the  air 
entering  the  furnace  is  probably  not  far  from  60°  F., 
while  the  temperature  of  the  flue  gases  in  uptake  or 
breeching  is  about  500°  F.  or  more.  Hence  this  excess 
air,  which  hasn't  helped  the  combustion  any,  and  has 
done  no  useful  work,  has  had  its  temperature  raised  at 
least  440°  F.,  and  this  takes  heat.  When  the  air  excess 
is  50  per  cent,  as  assumed  above,  it  takes  approxi- 
mately 13  per  cent  of  the  total  heat  in  the  fuel  to  heat 
up  this  air,  together  with  the  nitrogen  contained  in 
the  air  actually  used.  The  writer  has  tested  boiler 
furnaces  which  showed  CO2  as  low  as  3  per  cent ;  this 
means  about  600  per  cent  excess  air,  with  a  loss  of 
approximately  75  per  cent  of  all  the  heat  in  the  fuel. 
A  furnace  operated  in  such  a  manner  has  no  place 
in  a  steam  plant;  it  is  really  a  hot-air  heating  plant 
for  all  outdoors. 

One  point  to  be  kept  in  mind  in  connection  with 
heat  losses  through  excess  air  is  the  fact  that  as  the 
percentage  of  CO2  in  the  flue  gases  goes  down,  the 
heat  loss  goes  up,  but  not  proportionally.  Suppose, 
for  example,  that  a  test  shows  12  per  cent  CO2;  this 
means  about  75  per  cent  excess  air,  and  will  cause  a 
loss  of  about  17^2  per  cent  of  the  fuel.  Now  if  the 
CO2  be  raised  to  13  per  cent,  the  air  excess  becomes 
about  61.5  per  cent  and  the  heat  loss  16  per  cent. 
Thus  a  gain  of  1  per  cent  in  CCX  causes  a  saving  of 
\y2  per  cent  in  the  fuel.  On  the  other  hand,  take 
the  case  of  3  per  cent  CO2  cited  above ;  this  means 
600  per  cent  excess  air  and  a  loss  of  at  least  75  per 


FURNACE  EFFICIENCY  7 

cent  of  the  total  heat  of  the  fuel.  Now  if  the  CO2 
can  be  increased  to  4  per  cent,  we  shall  have  an  air 
excess  of  425  per  cent  and  a  heat  loss  of  about  58  per 
cent.  Thus  an  increase  of  1  per  cent  in  CO2  means  a 
saving  in  heat  of  approximately  17  per  cent.  So  the 
value  of  1  per  cent  of  CO2  depends  very  largely  upon 
where  it  is.  When  it  is  as  low  as  3  per  cent  or  4  per 
cent,  any  earnest  effort  to  decrease  air  excess  is  almost 
sure  to  result  in  increased  economy,  while  if  CO,  is 
in  the  neighborhood  of  12  per  cent  to  14  per  cent, 
large  increase  in  economy  is  not  possible. 

Volumes  of  hot  air  escaping  at  the  top  of  the 
smokestack  can  not  be  detected  by  the  eye,  and  for 
this  reason  the  question  of  air  excess  has  received 
much  less  attention  at  the  hands  of  the  engineer  than 
it  deserves.  All  other  furnace  losses  are  practically 
sure  to  be  small  compared  with  this  one,  and  yet  it 
is  the  last  one  to  receive  attention.  If  the  power-plant 
owner,  or  any  one  else  in  authority,  should  happen  to 
discover  a  large  amount  of  unburned  coal  in  the  ashes 
from  the  plant,  the  engineer  would  be  very  likely  to 
receive  a  call  from  the  office  and  be  asked  to  explain 
why  he  is  wasting  fuel.  Now  it  may  be  that  the  engi- 
neer is  a  thoroughly  competent  man  and  is  operating 
his  plant  at  maximum  efficiency,  but  the  boss  can 
see  that  coal  in  the  ashes,  and  it  looks  like  poor  econ- 
omy to  him.  But  let  us  consider  a  minute  and  we 
may  see  that  the  man  in  the  plant  is  a  better  engineer 
than  the  man  in  the  office.  One  of  the  most  fruitful 
sources  of  excess  air  is  holes  in  the  fire;  if  the  fire 
burns  through  in  spots  vast  quantities  of  cold  air 
rush  through  the  holes  and  furnace  efficiency  is  seri- 
ously impaired.  To  prevent  holes  in  the  fire  it  is 
often  necessary  to  carry  a  slightly  thicker  bed  of  fuel 
on  the  grates  than  would  otherwise  be  necessary. 
This  is  particularly  true  of  the  chain-grate  stoker, 
which  is  coming  into  such  general  use,  The  fuel  bed 


8  FURNACE  EFFICIENCY 

must  be  thick  enough  to  prevent  the  fire  from  burning 
off  at  the  back  of  the  grate.  It  is  good  economy  to 
do  this  even  at  the  expense  of  running  some  unburned 
coal  off  the  end  of  the  grate  into  the  ash  pit.  As  much 
as  50  per  cent  combustible  in  the  ash  may  be  more 
economical  and  an  evidence  of  better  operating  engi- 
neering than  an  ash  pit  which  shows  no  combustible 
at  all. 

Questions  and  Answers. 

Q.     What  is  the  function  of  a  boiler  furnace? 

A.  To  transform  the  heat  energy  of  the  coal  into 
a  form  available  to  the  boiler. 

Q.     What  is  the  function  of  the  steam  boiler? 

A.  To  take  the  heat  from  the  furnace  and  use  it 
in  the  generation  of  steam. 

Q.  Is  the  evaporative  test  a  good  one  to  deter- 
mine furnace  efficiency? 

A.     No. 

Q.     Why  not? 

A.  Because  evaporation  depends  upon  both  fur- 
nace and  boiler,  and  is  a  measure  of  their  combined 
efficiency. 

Q.     How  may  we  define  an  efficient  furnace? 

A.  An  efficient  furnace  is  one  which  consumes  all 
the  combustible  in  the  fuel  with  the  least  possible 
excess  of  air. 

Q.  How  can  we  tell  how  much  excess  air  a  fur- 
nace is  getting? 

A.  By  an  analysis  of  the  gases  coming  from  the 
fire. 

Q.     What  is  the  chief  combustible  part  of  coal? 

A.     Carbon. 

Q.  In  the  combustion  process,  what  becomes  of 
this  carbon? 

A.  It  unites  with  the  oxygen  of  the  air  to  form 
carbon  dioxid,  CO2. 


FURNACE  EFFICIENCY  9 

Q.  What  is  the  maximum  amount  of  CO2  that  it 
is  possible  to  have  in  the  boiler  furnace  gases? 

A.     21  per  cent. 

Q.     Is  this  ever  realized  in  practice? 

A.  No ;  excess  air  is  always  used,  and  this  reduces 
the  percentage  of  CO2. 

Q.  What  is  the  effect  of  excess  air  on  furnace 
efficiency? 

A.     It  reduces  the  efficiency. 

Q.     Why  is  this? 

A.  Because  of  the  large  amount  of  heat  required 
to  heat  the  excess  air. 

Q.  How  can  the  percentage  of  excess  air  be  calcu- 
lated from  the  CO2  in  the  flue  gases? 

A.  Subtract  the  percentage  of  CO2  from  21 ; 
divide  the  remainder  by  the  percentage  of  CO2 ;  mul- 
tiply this  result  by  100. 

Q.  What  percentage  of  C(X  represents  good  prac- 
tice? 

A.     From  12  per  cent  to  14  per  cent. 

Q.  Why  is  excess  air  such  a  common  cause  of 
low  furnace  efficiency? 

A.  Because  it  can  not  be  seen,  and  its  effect  is 
therefore  not  readily  realized. 

Q.     How  much  heat  is  lost  in  this  way? 

A.  From  12  per  cent  to  75  per  cent  of  the  total 
heat  in  the  fuel. 

Q.  Does  unburned  coal  in  the  ashes  mean  as  large 
a  loss  as  excess  air? 

A.  No;  50  per  cent  combustible  in  the  ash  may 
be  more  economical  than  holes  in  the  fire,  which 
cause  large  excess  of  air. 


10  FURNACE  EFFICIENCY 


CHAPTER  II. 

It  has  been  shown  that  the  only  reliable  index  of 
furnace  efficiency,  as  distinguished  from  combined 
furnace  and  boiler  efficiency,  is  to  be  found  in  the  flue- 
gas  analysis.  The  question  of  how  to  make  this 
analysis  is  therefore  one  of  importance,  and  should  be 
understood  by  every  engineer. 

Perhaps  the  best  known  and  most  widely  used 
equipment  on  the  market  for  this  purpose  is  the  Orsat 
gas-analysis  apparatus,  as  shown  in  Fig.  1.  As  usually 
made,  this  apparatus  is  designed  to  test  for  carbon 
dioxid  (CO2),  oxygen  and  carbon  monoxid  (CO).  The 
essential  parts  of  the  apparatus  are  the  three  U-shaped 
bottles,  A,  B  and  C;  the  measuring  burette  D,  and 
the  leveling  bottle  E.  It  will  be  seen  from  the  figure 
that  the  bottles  A,  B  and  C  really  consist  of  two  bot- 
tles each,  connected  at  the  bottom  with  a  bent  tube  of 
glass.  Also  it  will  be  noted  that  the  bottle  on  one 
side  is  closed  with  a  rubber  stopper,  through  which  a 
small  glass  tube  passes  to  act  as  an  air  vent,  while 
the  other  bottle  has  a  long  glass  stem  provided  with 
a  plug  cock  of  ground  glass.  The  measuring  burette 
is  provided  with  a  scale,  reading  in  cubic  centimeters, 
the  capacity  of  the  burette  being  100  cu.  cms.  The 
zero  of  the  scale  is  at  the  bottom,  where  it  will  be  seen 
that  the  burette  is  made  of  comparatively  small  diam- 
eter, so  as  to  give  a  more  open  scale.  At  its  top  the 
burette  D  is  drawn  down  into  a  small  tube  and  con- 
nected with  a  piece  of  rubber  tubing  H  to  the  glass 
header  F,  G.  This  header  is  a  tube  of  very  small  bore, 
so  that  its  capacity  is  negligible  as  compared  with  that 
of  the  measuring  burette  D, 


FURNACE  EFFICIENCY 


11 


The  leveling  bottle  E  is  connected  with  a  rubber 
tube  to  the  bottom  of  the  burette  D.  This  is  for  the 
purpose  of  drawing  flue  gas  into  the  measuring  bu- 


FIG.  i. 

rette  and  expelling  it  again,  which  is  done  by  lowering 
or  raising  the  leveling  bottle.  Each  of  the  U-shaped 
treating  bottles,  A,  B  and  C,  is  connected  to  the  glass 


12  FURNACE  EFFICIENCY 

header  F,  G,  so  that  they  may  be  connected  to  the 
source  of  gas  supply  at  F  or  to  the  measuring  burette 
D  as  may  be  desired. 

The  treating  bottle  A  contains  a  solution  of  caustic 
potash,  which  removes  the  CO2  from  the  flue  gas. 
Bottle  B  contains  a  solution  of  potassium  pyrogallate, 
which  removes  the  free  oxygen  from  the  gas,  and  bot- 
tle C  contains  a  saturated  solution  of  cuprous  chlorid 
for  removing  CO.  These  chemicals  may  be  obtained 
at  any  chemical  supply  house,  and  at  most  drug  stores. 
The  solutions  may  be  prepared  as  follows : 

The  caustic  potash  solution  may  be  prepared  by 
dissolving  one  pound  of  commercial  caustic  potash 
in  1,000  c.  c.  of  water.  Considerable  heat  is  evolved 
when  the  potash  is  dissolved  in  the  water,  and  for 
that  reason  the  bottle  should  be  placed  where  no  dam- 
age will  be  done  if  it  should  break.  Care  should  be 
taken  to  keep  the  potash  solution  from  coming  into 
contact  with  the  hands  or  the  clothing.  It  is  a  power- 
ful alkali,  which  is  extremely  unpleasant  when  it  gets 
on  the  hands,  and  will  destroy  the  clothing  almost  as 
quickly  as  an  acid.  When  the  solution  is  cold  it  should 
be  put  into  a  stock  bottle,  which  can  be  drawn  on  from 
time  to  time  as  needed. 

To  make  the  potassium  pyrogallate,  take  100  c.  c. 
of  the  potash  solution  already  prepared  and  add  to  it 
five  grams  of  pyrogallic  acid.  This  acid  comes  in  the 
form  of  a  white  powder,  which  dissolves  readily  in 
the  potash  solution.  After  a  little  experience  it  will 
not  be  necessary  to  weigh  the  five  grams  of  pyrogallic 
acid,  as  the  proper  amount  can  be  estimated  with  suffi- 
cient accuracy  by  simply  pouring  it  into  the  palm  of 
the  hand.  It  must  be  remembered  that  this  "  pyro  " 
solution  has  a  strong  affinity  for  oxygen,  and  hence 
it  must  be  kept  away  from  the  air  in  a  stoppered  bottle. 

The  cuprous  chlorid  solution  for  removing  the  CO 
is  the  most  difficult  of  all  the  reagents  to  prepare,  and 


FURNACE  EFFICIENCY  13 

is,  perhaps,  the  most  unsatisfactory  in  its  action.  First 
prepare  about  two  liters  of  dilute  hydrochloric  acid, 
specific  gravity  1.10,  by  diluting  muriatic  acid  with  an 
equal  volume  of  water.  Then  select  a  large  bottle  of 
at  least  two  liters  capacity  and  cover  the  bottom  about 
*/2  inch  deep  with  copper  oxid.  Then  add  a  number  of 
pieces  of  copper  wire  long  enough  to  reach  from  the 
bottom  to  the  top  of  the  bottle.  These  wires  should 
make  a  bundle  about  an  inch  in  diameter.  Now  fill 
the  bottle  with  the  dilute  hydrochloric  acid  and  wait 
for  the  copper  to  dissolve  in  the  acid.  Shake  the  bottle 
occasionally,  to  keep  the  contents  well  mixed.  When 
the  solution  has  become  colorless,  or  nearly  so,  it 
should  be  poured  into  a  smaller  stock  bottle  ready  for 
use.  This  stock  bottle  should  contain  some  pieces  of 
copper  wire  to  keep  the  solution  saturated.  Many 
chemical  supply  houses  keep  this  cuprous  chlorid  solu- 
tion in  stock,  and  the  average  user  will  probably  find 
it  more  satisfactory  to  buy  the  solution  already  pre- 
pared, when  possible.  It  must  be  protected  from  both 
air  and  sunlight,  which  cause  it  to  become  weak  and 
turn  dark. 

All  the  reagents  having  been  prepared,  the  appa- 
ratus can  now  be  made  ready  for  the  flue-gas  test. 
Pour  the  caustic  potash  into  treating  bottle  A  until 
the  solution  stands  about  half  way  up  in  both  limbs 
of  the  bottle.  Pour  bottles  B  and  C  half  full  with 
"  pyro  "  and  cuprous  chlorid  respectively.  We  must 
now  bring  the  solutions  in  the  front  limb  of  the  treat- 
ing bottles  to  exactly  the  same  level.  The  proper 
level  is  indicated  by  a  mark  on  the  glass  stem  at  the 
top  of  the  bottle.  The  bore  of  the  stem  at  this  point 
is  very  small,  so  that  a  slight  inaccuracy  in  the  level 
of  the  solution  will  not  cause  any  appreciable  error. 
Suppose  that  we  wish  to  raise  the  solution  in  the 
front  limb  of  bottle  A  to  the  mark  on  the  glass  stem. 
Open  the  valve  K  in  the  header  F,  G  and  raise  the 


14  FURNACE  EFFICIENCY 

leveling  bottle  E.  This  will  fill  the  measuring  burette 
D  with  water,  the  air  which  it  contains  being  forced 
out  at  F.  Now  close  the  valve  K  and  open  the  one 
over  bottle  A,  marked  R.  Lower  the  leveling  bottle 
E,  causing  the  water  level  to  fall  in  burette  D.  This 
will  reduce  the  pressure  over  the  solution  in  the  front 
limb  of  bottle  A  and  the  liquid  will  rise  there,  and  fall 
in  the  rear  limb.  Continue  to  lower  the  leveling  bot- 
tle until  the  solution  reaches  the  mark  on  the  stem, 
and  then  close  valve  R.  In  the  same  way  the  solu- 
tions in  the  other  treating  bottles  should  be  brought 
to  the  proper  level.  The  apparatus  is  now  ready  to 
make  the  analysis. 

Slip  a  piece  of  rubber  tubing  over  the  end  of  the 
glass  tube  at  F  and  connect  the  free  end  of  the  tube 
to  the  pipe  which  is  to  supply  the  flue  gas.  A  pinch 
cock  on  this  rubber  tube  will  be  of  service.  The  three- 
way  cock  K  should  then  be  opened,  while  cocks  R,  S 
and  T  are  closed.  Raise  the  leveling  bottle  E,  thus 
filling  the  burette  D  with  water  and  forcing  all  the 
air  out  at  W.  Raise  the  leveling  bottle  until  water 
reaches  the  point  G,  but  do  not  force  any  of  it  out  at 
W.  Now  turn  the  three-way  cock  K  so  as  to  open 
up  to  the  pipe  from  the  flue  connected  at  F.  The  out- 
let at  W  will  then  be  closed.  Lower  the  bottle  E  and 
thus  draw  in  a  charge  of  gas  from  the  flue.  Continue 
to  lower  the  leveling  bottle  until  the  water  in  the 
measuring  burette  D  falls  below  the  level  of  the  zero 
on  the  scale.  Now  place  the  pinch  cock  on  the  rubber 
tube  connected  at  F,  thus  closing  the  connection  to 
the  flue.  Open  cock  K  to  the  atmosphere  and  slowly 
raise  the  leveling  bottle  E  until  the  water  in  burette 
D  reaches  the  zero  on  the  scale.  This  will  force  a 
small  amount  of  gas  out  at  W,  and  we  shall  have  left 
just  100  c.  c.  under  atmospheric  pressure.  Close  the 
three-way  cock  K. 

Thus  far  our  attention  has  been  confined  to  getting 


FURNACE  EFFICIENCY  15 

a  sample  of  gas  for  analysis.  We  shall  now  proceed 
with  the  analysis  itself.  Open  the  cock  R,  raise  the 
leveling  bottle  E,  and  thus  force  the  gas  sample  out 
of  the  burette  D  and  into  the  treating  bottle  A  con- 
taining the  caustic  potash  solution.  The  potash  will 
be  forced  almost  entirely  out  of  the  front  limb  of  the 
bottle  and  into  the  rear  one.  In  most  forms  of  the 
Orsat  apparatus  the  front  limb  of  the  treating  bottle 
is  filled  with  a  bundle  of  small  glass  tubes.  These 
tubes  become  wet  with  the  chemical  and  offer  a  large 
surface  for  absorption  of  the  gas.  Allow  the  gas  to 
remain  in  treating  bottle  A  for  about  a  half  minute, 
then  lower  the  leveling  bottle  and  draw  the  gas  back 
into  the  measuring  burette.  This  will  cause  the  solu- 
tion to  rise  again  in  the  front  limb  of  bottle  A  and 
wet  the  small  glass  tubes  on  the  inside  with  fresh 
potash.  Then  force  the  gas  back  again  into  A  and 
repeat  the  operation  several  times.  In  order  to  get 
a  complete  absorption  of  CO2  the  gas  must  be  kept 
well  agitated,  which  can  be  accomplished  by  passing 
the  gas  frequently  between  the  burette  and  the  treating 
bottle. 

When  it  is  thought  that  the  CO2  has  been  all 
absorbed,  pass  the  gas  back  into  D,  lowering  E  until 
the  solution  in  A  rises  to  the  mark  on  the  stem  where 
it  was  before.  Close  cock  R.  Now  bring  the  surface 
of  the  water  in  E  to  the  same  level  as  that  in  D.  This 
can  be  done  by  sighting  across  the  surface  of  the  water 
in  E  and  is  for  the  purpose  of  insuring  normal  atmos- 
pheric pressure  on  the  gas  remaining  in  D.  It  will 
be  noted  that  there  is  less  gas  than  before,  the  water 
level  now  standing  above  the  zero  of  the  scale.  If  the 
water  level  stands  at  10  on  the  scale  it  means  that 
10  c.  c.  of  CO2  has  been  absorbed,  which  is  10  per 
cent  of  the  total  100  c.  c.,  with  which  we  started.  The 
gas  may  now  be  passed  into  bottle  A  again,  and  if 
when  it  is  returned  to  D  the  water  level  still  stands 


16  FURNACE  EFFICIENCY 

at  10  on  the  scale,  one  may  be  sure  that  all  the  CO2  is 
absorbed. 

The  remaining  gas  is  next  passed  into  bottle  B, 
where  the  free  oxygen  is  absorbed.  The  procedure  is 
exactly  the  same  as  for  CO2.  Suppose  that  after  all 
the  oxygen  has  been  absorbed  the  scale  reads  19.5  per 
cent.  This  means  that  CO2  plus  oxygen  equals  19.5 
per  cent ;  but  since  the  CO2  has  already  been  shown  to 
be  10  per  cent,  it  leaves  9.5  per  cent  for  oxygen. 

Next  pass  the  gas  into  bottle  C,  where  the  CO  is 
absorbed.  This  gas  is  usually  present  in  flue  gases, 
in  very  small  quantities,  if  at  all,  and  its  determination 
must  be  made  with  care  to  insure  accuracy.  The 
method  is  exactly  the  same  as  for  the  other  gases.  If 
the  reading  on  the  scale  after  the  CO  has  been  ab- 
sorbed is  20^4  per  cent,  the  amount  of  CO  is  evidently 
20>4  —  l9*/2  =  24  per  cent,  the  19^  per  cent  being 
the  sum  of  CO2  and  oxygen  already  determined. 

The  chemical  reagents  used  with  the  Orsat  appa- 
ratus will  wear  out  after  a  time  and  must  be  replaced. 
The  caustic  potash  solution  will  absorb  about  forty 
times  its  volume  of  CO0.  If  the  treating  bottle  A  con- 
tains 100  c.  c.  of  the  po"tash,  it  will  dissolve  40  X  100 
=  4,000  c.  c.  of  CO2.  If  the  average  amount  of  CO2 
in  the  flue  gas  were  10  per  cent,  that  is,  10  c.  c.  to  every 
100  c.  c.  of  gas,  then  the  caustic  potash  would  be  good 
for  about  four  hundred  tests. 

The  capacity  of  the  potassium  pyrogallate  solution 
to  absorb  oxygen  is  much  less,  1  c.  c.  of  the  "  pyro  " 
being  able  to  absorb  only  2  c.  c.  of  oxygen.  If  we 
assume  again  10  per  cent  CO2  and  about  10  per  cent 
of  oxygen  as  the  average,  then  the  potassium  pyro- 
gallate must  be  replaced  after  twenty  tests. 

The  cuprous  chlorid  will  absorb  only  its  own  vol- 
ume of  CO,  but  since  the  CO  is  present  in  flue  gas  in 
such  small  quantities  the  solution  is  good  for  a  large 
number  of  tests,  provided  it  is  not  exposed  to  air  and 


FURNACE  EFFICIENCY  17 

sunlight.  It  is  well  not  to  work  the  solutions  to  the 
limit,  but  to  replace  them  when  they  begin  to  grow 
weak.  Weakness  of  the  solutions  will  be  indicated 
by  an  increasing  amount  of  time  required  to  complete 
the  absorption  of  the  various  gases. 

One  very  important  point  in  flue-gas  analysis  is 
the  obtaining  of  a  sample  for  test  which  shall  be  a 
fair  average  of  all  the  gas  in  the  flue.  A  number  of 
rather  elaborate  and  costly  devices  for  drawing  off 
the  test  sample  have  been  devised,  none  of  which  the 
average  engineer  is  likely  to  use.  The  writer  is  of  the 
opinion  that  a  single  pipe  or  tube,  open  at  the  end,  and 
perforated  throughout  a  portion  of  its  length,  will  give 
a  very  fair  average  sample  of  the  gas.  This  pipe  should 
be  placed  in  the  boiler  pass,  uptake,  breeching,  or  wher- 
ever the  gas  sample  is  to  be  drawn,  with  its  open  end 
at  the  point  where  the  gas  velocity  is  greatest.  Wher- 
ever the  pipe  is  inserted  care  must  be  taken  not  to 
allow  a  large  leakage  of  air  into  the  boiler  setting  to 
dilute  the  sample.  If  the  pipe  is  inserted  through  an 
inspection  or  a  clean-out  door,  don't  leave  the  door 
ajar.  Use  every  possible  precaution  to  keep  the  air 
out.  If  the  sampling  pipe  is  inserted  through  a  hole 
in  the  breeching,  make  the  hole  just  large  enough  for 
the  pipe. 

When  drawing  a  sample  in  this  way  for  use  with 
the  Orsat  apparatus,  care  must  be  taken  to  draw  all 
the  air  from  the  pipe  and  its  rubber  hose  connection 
before  beginning  to  make  an  analysis.  This  can  best 
be  done  by  discarding  the  first  four  or  five  samples 
of  gas  which  are  drawn  into  the  apparatus  by  simply 
discharging  them  through  the  three-way  cock  K,  Fig. 
1,  into  the  atmosphere.  In  this  way  all  the  air  in  the 
sampling  pipe  and  its  connection  is  drawn  out  and  a 
good  sample  of  gas  obtained. 

Fig.  2  shows  an  extremely  compact  and  handy  flue- 
gas  apparatus  designed  by  Mr.  Joseph  W.  Hays.  It 


18 


FURNACE  EFFICIENCY 


FIG.  2. 


consists  of  measuring  burette,  reagent  bottles  for  de- 
termination of  CO2,  oxygen  and  CO,  much  the  same 
as  the  Orsat  apparatus.  The  leveling  bottle  L  is  con- 
nected to  the  bottom  of  the  measuring  burette  B  and 


FURNACE  EFFICIENCY  19 

is  used  in  exactly  the  same  way  as  in  the  Orsat.  One 
good  feature  of  this  apparatus  is  the  rubber  tube  and 
bulb  A,  connected  between  the  top  of  the  measuring 
burette  and  the  gas-sampling  pipe.  With  the  leveling 
bottle  L  filled  with  water,  gas  may  be  drawn  from  the 
flue  through  the  measuring  burette  B  by  simply  press- 
ing bulb  A  until  it  bubbles  through  the  water  in  L. 
In  this  way  a  large  amount  of  gas  may  be  drawn 
through  the  apparatus  and  discharged  until  a  good 
sample  of  gas  is  obtained.  This  Hays  apparatus  is 
smaller  and  more  compact  than  the  Orsat,  contains 
less  glass,  and  is  therefore  not  so  easily  broken,  and 
is  put  up  in  portable  form. 

Questions  and  Answers. 

Q.  What  is  the  best  known  apparatus  for  boiler- 
flue-gas  apparatus? 

A.     The  Orsat. 

Q.  What  gases  are  usually  determined  with  this 
apparatus? 

A.     CO.,,  CO  and  free  oxygen. 

Q.  What  chemicals  are  used  to  dissolve  or  absorb 
these  gases? 

A.  Caustic  potash  for  CO2,  potassium  pyrogallate 
for  oxygen,  and  cuprous  chlorid  for  CO. 

Q.  How  large  a  sample  of  flue  gas  is  tested  in  the 
Orsat  apparatus? 

A.     100  c.  c. 

Q.     How  is  this  gas  sample  measured? 

A.     In  a  graduated  measuring  burette. 

Q.  What  important  point  must  be  kept  in  mind 
when  measuring  the  gas? 

A.     To  measure  it  under  atmospheric  pressure. 

O.     How  can  this  be  done? 

A.  By  having  the  three-way  cock  open  to  the 
atmosphere  when  the  final  leveling  is  made. 


20  FURNACE  EFFICIENCY 

O.  Before  beginning  the  test  where  must  the 
chemicals  stand  in  the  reagent  bottles? 

A.  The  surface  of  the  chemical  must  stand  at  the 
mark  on  the  neck  of  the  bottle. 

Q.  Must  the  chemicals  be  brought  back  to  this 
same  point  when  the  test  is  finished? 

A.     Yes. 

Q.     How  much  CO2-  will  caustic  potash  absorb? 

A.     About  forty  times  its  volume. 

Q.  How  much  oxygen  will  potassium  pyrogallate 
absorb? 

A.     Twice  its  volume. 

Q.     How  much  CO  will  cuprous  chlorid  absorb? 

A.     An  amount  equal  to  its  volume. 

Q.     How  should  the  gas  be  drawn  from  the  flue? 

A.  Through  a  single  pipe,  open  at  the  end  and 
perforated  for  a  portion  of  its  length. 

Q.  Will  the  first  charge  drawn  into  the  Orsat 
apparatus  be  a  fair  sample  of  the  gas? 

A.  No ;  it  will  probably  contain  air  drawn  from 
the  sampling  pipe. 

Q.  What  should  be  done  with  this  first  sample  of 
gas? 

A.  It  should  be  blown  out  to  the  atmosphere 
through  the  three-way  cock. 

•Q.     How  many  charges  should  be  wasted  in  this 
way? 

A.  Probably  four  or  five;  at  least  until  the  oper- 
ator is  sure  that  all  the  air  has  been  drawn  from  the 
sampling  pipe. 


FURNACE  EFFICIENCY  21 


CHAPTER  III. 

It  has  been  shown  that  the  most  efficient  boiler 
furnace  is  the  one  that  consumes  all  the  combustible 
in  the  fuel  with  the  least  excess  of  air.  It  has  also 
been  explained  that  only  by  means  of  the  flue-gas 
analysis  can  the  engineer  tell  how  much  excess  air 
is  passing  through  his  furnace.  We  shall  assume, 
then,  that  these  two  facts  are  well  understood,  and 
also  that  the  method  of  making  the  flue-gas  test,  as 
explained  in  Chapter  II,  is  fully  mastered.  Let  us  now 
consider  how  an  engineer  can  make  a  practical  appli- 
cation of  these  principles  to  improve  the  efficiency  of 
his  boiler  furnace. 

He  must  first  supply  himself  with  a  hand  flue-gas 
instrument,  of  which  there  are  a  number  of  good 
makes  on  the  market,  the  average  cost  of  which  is 
probably  not  far  from  $30.  A  good,  reliable  draft 
gauge  will  be  found  extremely  desirable,  and  will 
probably  cost  about  $10.  A  thermometer  to  give  the 
temperature  of  the  flue  gases  will  be  of  much  assist- 
ance; instruments  specially  designed  for  this  pur- 
pose are  on  the  market,  but  any  reliable  thermometer 
can  be  used,  and  will  prove  less  expensive  than  the 
special  flue-gas  instrument.  A  thermometer  suffi- 
ciently accurate  for  all  practical  purposes  can  prob- 
ably be  bought  for  about  $5.  These  three  items  of 
expense  will  comprise  the  whole  outlay  for  apparatus, 
and  if  properly  used  the  instruments  will  pay  for 
themselves  many  times  over  in  reduced  coal  bills. 

Begin  with  the  flue-gas  apparatus,  to  determine 
just  what  kind  of  a  furnace  you  have,  whether  good, 


22  FURNACE  EFFICIENCY 

bad  or  indifferent,  from  a  standpoint  of  efficiency. 
Make  a  flue-gas  test  on  the  boiler  side  of  the  damper ; 
if  the  conditions  are  about  as  they  are  in  the  average 
plant,  about  7  per  cent  or  8  per  cent  of  CO2  will  be 
found  in  the  flue  gases.  Now  put  the  sampling  pipe 
into  the  first  pass  of  the  boiler  if  it  be  a  water-tube 
boiler,  or  at  the  rear  tube  sheet  if  it  be  a  horizontal 
tubular  boiler.  This  will  give  a  sample  of  the  fur- 
nace gases  just  as  they  leave  the  combustion  space 
of  the  furnace  and  before  they  come  into  contact  with 
the  heating  surfaces  of  the  boiler.  It  will  probably 
be  found  that  the  percentage  of  CO2  at  this  point  is 
somewhat  greater  than  was  found  just  below  the 
damper.  The  only  explanation  for  this  state  of  affairs 
is  that  the  furnace  gases  are  being  diluted  as  they  pass 
through  the  boiler.  This  dilution  of  the  gases  is 
caused  by  air  leaking  into  the  setting  through  cracks 
in  the  brickwork.  It  is  easy  to  underestimate  the 
amount  of  this  air  leakage,  many  engineers  believing 
that  it  has  practically  no  effect  upon  furnace  efficiency. 
Unless  your  brickwork  is  better  than  the  average,  you 
will  probably  find  from  1  per  cent  to  2  per  cent  less 
CO2  at  the  damper  than  at  the  first  pass,  and  this 
difference  is  due  entirely  to  air  leakage. 

If  this  is  found  to  be  the  case,  attention  must  be 
given  to  the  brickwork,  to  make  it  just  as  nearly  air- 
tight as  possible.  When  it  is  remembered  that  the 
average  air  pressure  inside  the  setting  is  about  ^2 
inch  of  water  below  atmosphere,  and  that  all  the 
cracks  and  holes  in  the  brickwork  are  trying  to  sat- 
isfy that  partial  vacuum,  an  idea  may  be  gained  of  how 
large  an  amount  of  air  gets  in  in  this  way. 

These  leaks  must  be  located  and  stopped.  Take 
a  coal  oil  torch  and  go  carefully  over  all  the  brick- 
work; whenever  a  leak  is  found  the  flame  will  be 
drawn  into  the  crack,  showing  that  air  is  passing  in 
at  that  point.  Examine  particularly  around  clean-out 


FURNACE  EFFICIENCY  23 

and  inspection  doors,  along  the  line  where  the  brick- 
work closes  in  around  the  shell  in  the  case  of  a  tubu- 
lar boiler,  and  at  all  points  where  for  any  reason  the 
brickwork  may  be  defective.  If  there  are  two  or 
more  boilers  set  in  a  battery,  and  the  boiler  next  to 
the  one  under  examination  is  "  dead,"  examine  the 
dividing  wall  with  care.  Frequently  these  walls  are 
poorly  built  and  serious  leakage  may  occur  through 
them  when  one  boiler  is  out  of  service. 

The  moment  a  leak  is  discovered,  stop  it  up.  A 
pail  of  whitewash,  into  which  some  glue  has  been  dis- 
solved, will  make  a  good  filler  for  the  cracks.  Paint 
the  brickwork  over  generously  with  this  solution 
wherever  a  crack  is  found,  care  being  taken  to  work 
it  well  into  the  holes.  When  dry,  test  again  with 
the  torch  to  make  sure  that  the  leak  has  been  stopped. 
This  will  require  considerable  patience  and  involve 
work,  but  there  is  no  doubt  but  that  in  the  average 
boiler  plant  it  will  mean  a  saving  in  coal  large  enough 
to  make  all  the  work  and  trouble  decidedly  worth 
while. 

Many  engineers  are  so  convinced  of  the  importance 
of  a  tight  boiler  setting  that  they  provide  a  complete 
insulating  covering  for  the  brickwork.  Such  a  cov- 
ering may  be  made  as  follows :  Cover  the  surface  of 
the  setting  with  a  layer  of  asbestos  cement  or  plaster- 
from  1  inch  to  2  inches  thick;  cover  this  plaster  with 
canvas  and  then  apply  a  generous  coat  of  paint  to  the 
canvas.  This  produces  a  setting  which  is  as  near  air- 
tight as  it  is  possible  to  make  it,  and  while  it  is  con- 
siderably more  expensive  than  filling  the  cracks  with 
whitewash  and  glue,  it  makes  a  much  more  finished 
job  and  will  last  a  considerable  length  of  time. 

When  the  leaks  in  the  setting  have  been  stopped 
it  will  be  found  that  the  CCX  at  the  damper  is  prac- 
tically the  same  as  at  the  first  pass.  But  even  yet  the 
percentage  of  CO2  may  be  less  than  it  should  be  and 


X 

24  FURNACE  EFFICIENCY 

it  will  be  necessary  to  look  further  for  the  causes  of 
excess  air.  In  this  connection  a  careful  study  of  draft 
conditions  will  be  of  great  importance,  for  it  will 
assist  in  arriving  at  the  most  efficient  operating  con- 
ditions. 

Draft,  as  every  engineer  knows,  is  caused  by  the 
difference  in  weight  between  the  hot  gases  inside  the 
smoke  stack  and  a  column  of  air  of  equal  height  and 
diameter  outside  of  the  stack.  There  is,  therefore,  a 
difference  in  pressure  between  the  inside  of  the  fur- 
nace and  the  outside,  and  this  difference  in  pressure 
forces  air  through  the  furnace  and  boiler  and  up  the 
chimney.  The  function  of  the  draft  is  therefore  to 
supply  air  to  burn  the  fuel,  and  in  general  the  greater 
the  draft  the  more  fuel  can  be  burned.  If  the  draft 
in  any  particular  case  is  too  great,  an  excessive  amount 
of  air  will  be  forced  through  the  fuel  bed;  portions 
of  the  grate  will  be  burned  bare  of  coal,  producing 
holes  in  the  fire,  through  which  large  quantities  of 
air  will  rush,  thus  further  increasing  the  excess.  If 
the  draft  is  insufficient,  the  combustion  will  be  incom- 
plete with  the  formation  of  smoke  and  CO  in  the  flue 
gases,  and  it  will  be  impossible  to  carry  the  load. 

In  order  to  determine  what  is  the  proper  draft  for 
a  particular  boiler  operating  under  given  load  con- 
ditions, a  series  of  tests  must  be  made  with  the  flue- 
gas  apparatus  and  the  draft  gauge.  The  tendency  in 
many  cases  is  to  use  too  much  draft  rather  than  too 
little,  with  the  result  that  too  great  an  excess  of  air 
is  drawn  through  the  fuel  bed.  Measure  the  draft 
over  the  fire  and  at  the  same  time  make  an  analysis 
of  the  combustion  gases  from  the  first  pass  of  the 
boiler.  Then  either  increase  or  decrease  the  draft 
very  slightly  by  opening  or  closing  the  damper 
respectively,  and  again  observe  draft  and  CO.,.  If  the 
CO.,  has  increased  you  are  moving  in  the  right  direc- 
tion ;  if  not,  move'  in  the  opposite  direction.  In  this 


FURNACE  EFFICIENCY  25 

way,  by  making  very  small  changes  each  time,  dis- 
cover what  draft  gives  the  highest  possible  percentage 
of  CO.,  consistent  with  satisfactory  operation.  You 
must,  of  course,  carry  your  load,  no  matter  what  hap- 
pens to  the  CO2,  and  the  draft  must  not  be  reduced  to 
the  point  where  the  steam  gauge  begins  to  fall.  Also, 
when  reducing  the  draft,  watch  for  CO  in  the  flue 
gases;  this  indicates  incomplete  combustion,  and 
marks  the  point  beyond  which  draft  reduction  must 
not  be  carried. 

By  a  careful  study  of  flue  gas  and  draft  it  will  thus 
be  discovered  what  is  the  proper  draft  for  maximum 
efficiency  with  your  particular  load.  Note  the  posi- 
tion of  the  damper  and  keep  it  there  as  long  as  the  load 
remains  the  same.  When  the  load  changes,  a  differ- 
ent draft  and  a  different  position  of  the  damper  will 
be  necessary.  An  engineer  should  know  accurately 
how  much  draft  is  required  for  a  light,  medium  and 
heavy  load,  and  should  siee  that  the  damper  is  kept  in 
the  proper  position  to  give  that  draft.  Of  course,  it 
is  much  easier  to  operate  under  all  conditions  of  load 
with  a  wide-open  damper,  but  it  is  wasteful  of  coal, 
and  coal  costs  money. 

In  changing  the  draft  to  meet  varying  conditions 
of  operation,  it  is  usually  better  to  do  it  with  the 
damper  as  suggested  above,  rather  than  with  the  ash- 
pit doors.  If  the  draft  is  varied  by  means  of  the 
ash-pit  doors  while  the  damper  remains  wide  open  all 
the  time,  the  full  draft  of  the  stack  is  pulling  on  the 
furnace  continually.  If  the  ash-pit  doors  are  nearly 
closed,  the  effect  of  such  an  arrangement  is  to  greatly 
increase  the  amount  of  air  drawn  into  the  furnace  at 
all  other  points.  The  amount  of  air  drawn  in  over  the 
fire,  as  well  as  that  getting  in  at  any  imperfect  places 
in  the  setting,  will  be  increased.  On  the  other  hand,  if 
the  damper  be  partly  closed  when  less  draft  is  desired, 
the  "  pull  "  of  the  stack  will  be  reduced,  which  will 


26  FURNACE  EFFICIENCY 

cause  a  proportional  drop  in  the  draft  at  all  parts  of 
the  setting.  Thus  the  same  relative  amounts  of  air 
will  be  drawn  in  over  the  fire  and  under  it  as  before, 
so  that  combustion  conditions  will  remain  about  as 
they  were. 

The  relation  between  air  admitted  through  the  fire 
to  that  admitted  over  it  is  one  that  must  be  deter- 
mined by  each  engineer  for  his  particular  conditions. 
It  will  vary  considerably  with  the  method  of  firing 
and  the  kind  of  fuel  used.  A  bituminous  coal  which 
has  a  high  volatile  content  and  which  is  fired  by  hand 
requires  a  considerable  amount  of  air  over  the  fire. 
When  a  charge  of  such  coal  is  thrown  into  the  fur- 
nace a  large  volume  of  volatile  combustible  gas  is 
distilled.  Considerable  air  must  be  admitted  over  the 
fire  to  consume  this  gas,  otherwise  CO  and  smoke 
will  be  produced.  When  the  volatile  gas  has  all  been 
consumed  and  only  fixed  carbon  remains,  the  air  com- 
ing through  the  fire  will  be 'sufficient  for  combustion 
and  that  coming  in  over  the  fire  may  be  shut  off. 
Thus  in  a  hand-fired  furnace  the  amount  of  air  over 
the  fire  must  be  changed  from  time  to  time  to  suit 
conditions.  Here  again  the  flue-gas  apparatus  will  be 
a  reliable  indicator  of  furnace  conditions.  Too  much 
air  over  the  fire  will  be  just  as  serious  from  a  stand- 
point of  efficiency  as  too  much  through  it.  Discover 
by  means  of  the  flue-gas  test  the  proper  manner  of  air 
control  for  your  furnace  and  then  stick  to  it. 

It  has  been  pointed  out  that  too  much  draft  has  a 
tendency  to  burn  holes  in  the  fire  through  which  a 
large  amount  of  air  passes,  diluting  the  furnace  gases 
and  reducing  efficiency.  The  remedy  is  to  reduce  the 
draft  and  carry  a  thicker  fire.  In  the  case  of  a  boiler 
under  very  light  load  it  may  happen  that  if  the  fire 
is  thickened  much  the  safety  valve  will  blow  off,  while 
if  the  draft  is  reduced  enough  to  prevent  holes  in  the 
fire  imperfect  combustion  and  smoke  will  result. 


FURNACE  EFFICIENCY  27 

This  is  an  extremely  difficult  condition  under  which 
to  operate  a  boiler  furnace  efficiently,  because  there 
is  too  much  grate  surface  for  the  work  required  of 
the  furnace.  If  the  boiler  operates  habitually  under 
such  a  light  load,  steps  should  be  taken  to  reduce  the 
grate  area.  If,  however,  the  underload  occurs  only 
for  a  comparatively  small  portion  of  the  time,  all  that 
can  be  done  to  improve  efficiency  is  to  reduce  the  draft 
as  much  as  practicable  and  then  carry  as  uniform  a 
fire  as  possible,  care  being  taken  to  prevent  holes. 

A  boiler  served  with  a  chain-grate  stoker  and 
operated  under  a  light  load  is  almost  sure  to  show 
inefficient  combustion.  A  bare  space  a  foot  or  more 
in  width  will  be  seen  at  the  back  of  the  grate  as  well 
as  holes  here  and  there  in  the  fire.  Since  the  grate 
surface  can  not  be  reduced,  there  is  no  remedy  except 
to  increase  the  load.  In  fact,  with  water-tube  boilers 
and  chain-grate  stokers  it  may  be  put  down  as  a  prac- 
tically invariable  rule  that  it  is  good  economy  to  oper- 
ate one  unit  at  50  per  cent  or  more  overload  than  two 
units  at  75  per  cent  of  rating. 

In  all  questions  about  air  supply  to  a  boiler  fur- 
nace, rely  on  the  flue-gas  apparatus  to  give  the  correct 
answer. 

Questions  and  Answers. 

Q.  Where  should  a  flue-gas  sample  be  taken  for 
analysis  to  show  combustion  conditions? 

A.     Usually  on  the  boiler  side  of  the  damper. 

Q.  What  would  a  test  at  the  first  boiler  pass 
show  ? 

A.  The  quality  of  the  gas  as  it  comes  from  the 
fire. 

Q.     Will  there  be  any  difference  in  the  gas  at  these 
two  points? 

A.  Yes;  the  CCX  will  usually  be  higher  at  the 
first  pass  than  at  the  damper. 


28  FURNACE  EFFICIENCY 

Q.     What  is  the  reason  for  this? 

A.     Infiltration  of  air  through  the  setting. 

Q.     How  may  the  leaks  in  the  setting  be  located? 

A.     With  a  flaming  torch ;  the  flame  will  be  drawn 
into  the  cracks  by  the  draft. 

Q.     How  may  the  leaks  be  stopped? 

A.     By  filling  them  with  whitewash  in  which  glue 
has  been  dissolved. 

Q.     How  may  a  boiler  setting  be  covered  to  pre- 
vent all  leakage? 

A.     With  asbestos  cement  or  plaster,  covered  with 
canvas  and  painted. 

Q.     What  is  the  function  of  draft  in  a  boiler  fur- 
nace? 

A.     To  burn  fuel. 

Q.     What  happens  when  the  draft  is  too  strong? 

A.     Holes  are   burned   in   the   fire,   and   efficiency 
goes  down. 

Q.     What  happens  when  the  draft  is  too  weak? 

A.     Imperfect  combustion  results,  with  the  forma- 
tion of  CO  and  smoke. 

Q.     How   may   the   proper  draft   conditions   for  a 
given  load  be  discovered? 

A.     By  flue-gas  analysis  at  different  drafts. 

Q.     How  should  the  draft  be  varied? 

A.     By  the  damper. 

Q.     Is  it  possible  to  operate  a  furnace  at  high  effi- 
ciency under  light  load? 

A.     No. 

Q.     Why  not? 

A.     There  is  too  much   grate  area  for  the  work 
required. 

Q.     Should  a  boiler  ever  be  worked  at  light  load 
if  it  can  be  avoided? 

A.     No ;    it  is  much  better  to  run  fewer  boilers  at 
an  overload. 


FURNACE  EFFICIENCY  20 


CHAPTER  IV. 

It  was  shown  in  a  previous  chapter  that  a  careful 
control  of  draft  is  absolutely  essential  to  high  fur- 
nace efficiency.  When  the  load  on  a  boiler  varies, 
the  amount  of  fuel  charged  into  the  furnace  is  varied 
in  proportion  to  the  load  demands.  If  good  efficiency 
of  combustion  is  to  be  maintained,  the  amount  of  air 
admitted  to  the  furnace  must  be  varied  in  practically 
the  same  proportion  as  the  coal,  so  that  combustion 
conditions  may  be  maintained  practically  constant. 
This  necessitates  a  careful  supervision  over  the  draft 
at  all  times,  and  under  all  conditions  of  load. 

It  has  been  pointed  out  that  the  proper  draft  for 
a  given  furnace,  using  a  given  quality  of  coal  and 
operating  under  a  given  load,  can  only  be  determined 
by  a  careful  study  of  the  flue  gas,  together  with  the 
draft-gauge  readings.  It  will  be  of  considerable 
assistance  in  determining  the  proper  draft  to  use 
under  any  set  of  conditions,  if  the  engineer  is  familiar 
with  average  draft-pressure  losses  through  a  few  of 
the  boilers  which  are  used  most  widely  in  commercial 
practice.  With  such  figures  at  hand  it  will  be  easier 
to  reach  good  conditions  in  any  particular  boiler. 
Also  sources  of  trouble,  such  as  faulty  design,  defect- 
ive baffles,  or  dirty  tubes,  may  be  located  simply  by 
an  analysis  of  the  draft-gauge  readings. 

Fig.  3  shows  a  horizontal  return  tubular  boiler 
served  with  a  chain-grate  stoker.  The  figures  in  the 
small  circles  show  the  average  value  of  the  draft  at 
that  particular  point,  expressed  in  inches  of  water. 
These  figures  are  the  average  taken  from  a  large 


30 


FURNACE  EFFICIENCY 


number  of  observations,  and  may  be  relied  upon  as 
fairly  representative  of  average  draft  conditions  in  a 
boiler  of  this  type.  It  should  be  observed,  however, 
that  the  absolute  values  given  are  not  of  so  much 
importance  as  a  guide  in  arriving  at  good  draft  con- 
ditions as  the  'relative  values.  For  example,  if  the 
load  on  the  boiler  were  to  decrease  considerably,  a 
thinner  fuel  bed  would  have  to  be  carried.  In  order 
to  prevent  too  great  a  quantity  of  air  being  drawn 
through  the  fire  the  damper  must  be  partially  closed. 
This  might  reduce  the  draft  at  the  front  tube  sheet 
from  0.52  to,  say,  0.40.  But  if  the  boiler  and  setting 
were  properly  designed  and  in  good  condition  there 
would  be  a  proportional  decrease  in  the  draft  at  all 
other  points.  Over  the  fire  it  would  probably  be 
reduced  to  about  0.23  instead  of  0.30. 

On  the  other  hand,  if  the  dampers  were  not  par- 
tially closed  when  the  load  decreased,  wasteful  fur- 
nace conditions  would  result  and  the  draft  readings 
would  show  it.  The  draft  at  the  front  tube  sheet 


FURNACE  EFFICIENCY  31 

would  still  remain  at  about  0.52  because  the  position 
of  the  damper  is  unchanged.  But  since  the  fuel  bed 
is  now  much  thinner  than  before,  the  pressure  drop 
through  it  would  be  much  less  than  it  was.  The  read- 
ing over  the  fire  would  be  reduced  to  0.20  or  even  less. 
Since  the  draft  below  the  damper  is  unchanged,  this 
would  mean  a  vast  excess  of  air  drawn  through  the 
thin  fire,  with  a  consequent  loss  in  furnace  efficiency. 
It  will  be  evident,  therefore,  that  much  may  be  learned 
about  furnace  and  boiler  conditions  by  a  study  of  the 
draft  at  various  points  in  the  setting.  If  the  draft 
readings  bear  the  same  general  relation  to  each  other 
as  is  shown  in  Fig.  3^the  conditions  are  about  right. 
Any  marked  departure  from  these  proportions  indi- 
cates poor  practice. 

Suppose,  for  example,  that  the  draft  in  the  com- 
bustion chamber  back  of  the  bridge  wall  were  found 
to  be  0.40  instead  of  0.33.  This  would  mean  too  great 
a  loss  of  draft  pressure  over  the  bridge  wall.  The 
only  explanation  for  such  a  state  of  affairs  is  that 
the  space  over  the  bridge  wall  is  too  small,  requiring 
a  high  gas  velocity  at  this  point  with  a  consequent 
large  drop  in  pressure.  The  remedy  is  to  provide 
greater  space  at  this  point  by  lowering  the  bridge 
wall.  In  general,  this  space  should  be  large  enough 
to  allow  for  a  maximum  gas  velocity  not  to  exceed 
35  to  40  feet  per  second.  If  the  maximum  rate  of 
combustion  for  the  furnace  has  been  predetermined 
(by  an  analysis  of  the  probable  load),  and  the  kind 
of  fuel  to  be  used  has  been  decided  upon,  it  is  possible 
to  calculate  the  volume  of  gases  which  must  pass 
over  the  bridge  wall,  furnace  temperature  being  taken 
into  account.  It  is  then  a  comparatively  simple  mat- 
ter to  calculate  the  area  required  over  the  bridge  wall. 
But  if  the  boiler  is  overloaded  more  than  was  orig- 
inally anticipated,  or  if  a  coal  is  used  which  has  a 
larger  volatile  content  than  was  expected,  then  the 


32  FURNACE  EFFICIENCY 

calculated  area  will  prove  insufficient.  The  result 
will  be  too  large  a  drop  in  draft  pressure  over  the 
bridge  wall,  which  can  be  detected  immediately  by 
means  of  the  draft-gauge  readings. 

In  like  manner  faulty  boiler  design  can  be  de- 
tected by  the  draft  readings.  If  the  tube  area  is  too 
small  the  draft  loss  through  the  boiler  will  be  exces- 
sive, while  if  it  is  too  large  the  draft  loss  will  be  less 
than  that  shown  in  the  figure.  Tubes  clogged  with 
soot  and  dirt  will  increase  the  loss  through  the  boiler, 
so  that  it  is  possible  to  tell  the  condition  of  the  tubes, 
to  a  certain  extent  at  least,  by  the  draft  readings. 

Fig.  4  shows  a  water-tube  boiler  of  the  B.  &  W. 
type,  served  with  a  chain-grate'  stoker,  and  with  the 
average  draft  readings  at  various  points  given.  It 
will  be  noted  that  the  draft  over  the  fire  in  this  case 
is  0.32,  just  one-half  of  what  it  is  at  the  damper.  This 
is  the  same  relation  as  was  shown  for  the  horizontal 
tubular  boiler  of  Fig.  3.  The  boiler  shown  in  this 
figure  is  vertically  baffled,  the  gases  passing  three 
times  across  the  tubes.  The  pressure  drop  is  fairly 
uniform  from  fire  to  damper,  showing  no  restricted 
portion  in  the  gas  passage,  and  no  short  circuit. 

A  boiler  baffled  in  this  way  does  not  readily  form 
short  circuits  through  which  the  gases  may  pass, 
because  there  are  no  points  in  close  proximity  to  each 
other  which  differ  widely  in  draft  pressure.  Consider, 
however,  what  would  take  place  if  the  front  baffle 
should  burn  through  at  the  bottom.  Instead  of  pass- 
ing up  across  the  tubes  the  gases  would  pass  through 
the  hole  in  the  baffle,  thus  finding  a  much  shorter  path 
to  the  stack.  The  result  would  be  a  serious  loss  in 
efficiency  because  the  gases  are  not  coming  in  contact 
with  the  tubes  as  they  should,  and  hence  do  not  give 
up  their  heat  properly.  A  fault  of  this  kind  will 
usually  be  made  apparent  to  one  who  understands 
the  situation  simply  from  the  draft  readings.  In  the 


FURNACE  EFFICIENCY 


33 


34  FURNACE  EFFICIENCY 

case  of  a  short  circuit  as  described  the  pressure  drop 
between  the  fire  and  the  rear  of  the  bridge  wall  would 
be  much  less  than  0.12,  as  shown  in  the  figure.  Such 
a  short  circuit  can  almost  always  be  located  by  a 
study  of  draft-pressure  drops  from  point  to  point 
through  the  setting  in  the  normal  path  of  the  gases. 

Restricted  passages  can  be  located  in  the  same 
way,  because  in  this  case  the  normal  draft-pressure 
drop  will  be  increased. 

Fig.  5  shows  a  Heine  boiler,  horizontally  baffled. 
This  boiler  is  quite  similar  to  the  B.  &  W.  horizon- 
tally baffled  type,  so  far  as  draft-pressure  losses  are 
concerned.  It  will  be  noted  in  this  case  that  the  total 
pressure  drop  through  this  boiler  is  greater  than 
through  the  vertically  baffled  unit.  The  ratio  between 
draft  over  the  fire  and  at  the  damper  is  almost  1  to  3, 
while  in  the  previous  case  it  is  1  to  2.  In  a  boiler 
baffled  in  this  way  the  gases  pass  to  the  near  of  the 
combustion  chamber  before  striking  the  tubes.  They 
then  pass  once  over  the  tubes  in  the  direction  of  their 
length  instead  of  across  the  tubes  as  in  the  previous 
case.  The  bottom  row  of  tubes  has  a  covering  of  fire- 
brick tile,  carried  back  to  within  3  or  4  feet  of  the  rear 
end.  This  forms  a  fire-brick  roof  for  the  furnace  and 
greatly  assists  in  the  combustion. 

A  boiler  baffled  in  this  way  has  a  tendency  to  de- 
velop short  circuits,  as  will  be  apparent  from  a  con- 
sideration of  the  figure.  Over  the  fire  the  draft 
pressure  is  0.28,  while  directly  above,  on  the  other 
side  of  the  tile  roof,  it  is  0.46.  The  same  condition 
exists  on  opposite  sides  of  the  baffle  on  the  top  row 
of  tubes.  Below  this  baffle  the  pressure  is  about  0.36, 
while  above  it  there  is  a  pressure  of  0.62.  Thus  there 
is  a  pressure  difference  on  opposite  sides  of  this  baffle 
of  0.26  inches,  which  tends  to  produce  a  short  circuit 
at  that  point.  For  this  reason  both  the  tile  roof  and 
the  upper  baffle  must  be  watched  closely  for  leaks, 


FURNACE  EFFICIENCY 


35 


36 


FURNACE  EFFICIENCY 


which  become  quite  serious  on  account  of  the  large 
pressure  differences.  Here  again  the  draft  gauge  fur- 
nishes the  information  as  to  conditions  inside  the 
setting,  if  one  is  able  to  interpret  these  readings. 

Fig.  6  shows  a  Stirling  boiler  with  the  draft-pres- 
sure readings  indicated.    It  will  be  noted  that  the  total 


FIG.  6. 


draft  loss  in  this  boiler  is  practically  the  same  as  in 
the  case  of  the  Heine  type,  horizontally  baffled.  The 
ratio  between  draft  over  the  fire  and  at  the  uptake  is 
practically  1  to  3,  the  same  as  for  the  Heine  boiler. 
An  inspection  of  the  figure  will  show  the  points  at 
which  short  circuits  through  the  baffles  are  most 


FURNACE  EFFICIENCY  37 

likely  to  occur.  Such  a  point  exists  at  the  lower  part 
of  the  first  baffle  just  above  the  bottom  drum.  The 
tendency  is  for  the  hot  gases  from  the  rire  to  pass 
back  over  the  bridge  wall,  through  the  first  bank  of 
tubes,  and  impinge  on  the  baffle  at  this  point.  The 
tile  becomes  cracked  and  burned  after  a  while  and 
a  leak  is  established.  Draft  readings  taken  over  the 
fire  and  in  the  bottom  of  the  second  bank  of  tubes 
will  furnish  reliable  information  as  to  the  condition 
of  the  baffle  at  this  point.  A  very  small  pressure 
drop  between  these  two  points  indicates  a  leak.  The 
second  baffle  may  be  examined  for  leaks  in  the  same 
way. 

In  all  the  figures  shown  thus  far  it  will  be  noted 
that  the  draft  over  the  fire  is  from  0.25  to  0.30.  As 
has  been  already  pointed  out,  this  will  vary  with  the 
thickness  of  the  fuel  bed.  In  general,  the  amount  of 
coal  which  can  be  burned  on  the  grate  depends  upon 
the  available  draft  over  the  fire.  Within  certain 
limits,  ten  pounds  of  coal  can  be  burned  per  square 
foot  of  grate  area  per  hour  for  each  0.1  inch  of  draft 
available  at  the  fire.  This  relation  holds  up  to  a  com- 
bustion rate  of  about  thirty  pounds  per  square  foot 
per  hour,  after  which  a  disproportionate  increase  in 
draft  is  required  for  a  given  increase  in  combustion 
rate.  The  drafts  given  in  the  figures  would  therefore 
make  possible  a  combustion  rate  of  from  twenty-five 
to  thirty  pounds  per  square  foot  per  hour.  When  it  is 
remembered  that  these  furnaces  are  served  with  chain- 
grate  stokers,  which  are  efficient  even  at  high  rates 
of  working,  this  rate  of  combustion  will  not  seem 
excessive. 

The  importance  of  accurate  information  in  regard 
to  normal  draft  conditions  in  the  different  boilers  is 
not  easily  overestimated.  One  is  then  in  a  position 
to  note  any  departure  from  normal  conditions,  and  to 
assign  a  reason  for  it.  With  the  possible  exception 


38  FURNACE  EFFICIENCY 

of  the  instrument  for  flue-gas  analysis,  there  is  no 
single  device  which  will  give  as  much  information 
about  furnace  and  boiler  conditions  as  the  draft  gauge, 
if  intelligently  used. 

Questions  and  Answers. 

Q.  Why  must  the  draft  be  regulated  carefully  as 
the  load  on  a  boiler  changes? 

A.  Because  the  air  admitted  to  the  furnace  must 
be  properly  proportioned  to  the  fuel  if  good  efficiency 
is  to  be  maintained. 

Q.  How  may  the  proper  draft  for  any  set  of  con- 
ditions be  determined? 

A.  •  By  means  of  the  flue-gas  analysis. 

Q.  Of  what  value  is  an  accurate  knowledge  of 
average  draft  conditions  throughout  a  boiler  setting? 

A.  It  makes  it  possible  to  locate  furnace  and 
boiler  troubles. 

Q.  How  would  tubes  or  flues  clogged  with  soot 
and  dirt  affect  the  draft  readings? 

A.  This  condition  would  be  indicated  by  an  abnor- 
mally large  draft-pressure  loss  between  the  front  and 
rear  tube  sheets. 

Q.  How  would  too  small  an  area  over  the  bridge 
wall  be  indicated  in  the  draft  readings? 

A.  By  too  large  a  drop  between  front  and  rear 
of  bridge  wall.  Such  a  condition  would  also  probably 
produce  hot  side  walls  and  grates,  due  to  the  bottling 
up  the  hot  gases  in  the  furnace. 

Q.  How  large  an  area  should  be  provided  over 
the  bridge  wall? 

A.  Large  enough  so  that  the  maximum  velocity 
of  the  gases  will  not  exceed  35  to  40  feet  per  second. 

Q.  How  would  a  leaky  or  broken  baffle  be  indi- 
cated by  the  draft  readings? 

A.  By  abnormally  low  draft-pressure  drop  be- 
tween opposite  sides  of  the  affected  baffle. 


FURNACE  EFFICIENCY  39 

Q.  What  is  the  chief  factor  determining  the 
amount  of  coal  which  can  be  burned  on  a  furnace 
grate  ? 

A.     The  amount  of  draft  available  over  the  fire. 

Q.  What  relation  is  there  between  available 
draft  and  rate  of  combustion? 

A.  About  ten  pounds  of  coal  can  be  burned  per 
square  foot  of  grate  area  per  hour  for  each  0.1  inch 
of  draft. 

Q.     Does  this  relation  hold  indefinitely? 

A.  Xo ;  when  the  rate  of  combustion  exceeds 
thirty  pounds  per  square  foot  per  hour  the  draft  must 
be  increased  faster  than  the  rate  of  combustion.  To 
burn  forty  pounds  of  coal  would  require  0.42  inch  of 
draft  at  least. 


40  FURNACE  EFFICIENCY 


CHAPTER  V. 

It  was  shown  in  an  earlier  chapter  that  an  efficient 
boiler  furnace  is  one  which  burns  all  of  the  combust- 
ible of  the  fuel  with  the  least  possible  excess  of  air. 
It  was  also  pointed  out,  however,  that  there  is  a  limit 
beyond  which  air  reduction  can  not  be  carried  without 
a  drop  in  efficiency.  This -loss  in  efficiency  is  due  to 
incomplete  combustion,  the  most  noticeable  effect  of 
which  is  the  production  of  smoke.  But  smoke  is  only 
the  visible  effect  of  incomplete  combustion,  and  is 
usually  less  serious  from  the  standpoint  of  efficiency 
than  the  invisible  effects,  of  which  the  smoke  is  the 
sign. 

The  Formation  of  Smoke. 

When  coal  is  fed  into  a  boiler  furnace,  either  by 
hand  or  mechanically,  the  first  effect  of  the  heat  is  to 
drive  off  the  volatile  gases  which  all  coal  contains  in 
larger  or  smaller  amounts.  Anthracite  coal  may  con- 
tain as  low  as  3  per  cent  of  these  volatile  gases,  while 
lignite  may  contain  as  much  as  50  per  cent.  They  are 
composed  of  hydrogen  and  carbon  united  in  different 
proportions,  and  are  usually  referred  to  under  the 
comprehensive  term,  "  hydrocarbons." 

The  exact  chemical  action  which  takes  place  in  the 
furnace  when  these  hydrocarbons  are  brought  into 
contact  with  air  is  probably  not  definitely  understood. 
It  appears,  however,  that  at  the  temperature  of  the 
furnace  some  of  these  gases  may  be  broken  up  into 
the  elements  of  which  they  are  composed ;  that  is,  into 
carbon  and  hydrogen.  The  latter  element  promptly 


FURXACE  EFFICIENCY  41 

unites  with  the  oxygen  of  the  entering  air,  forming 
water  vapor.  If  there  is  an  abundant  supply  of  air 
present,  the  free  carbon  also  unites  with  the  oxygen 
to  form  CO2.  But  if  the  air  supply  is  insufficient,  part 
of  the  carbon  will  form  CO  instead  of  CO,,  and  part 
of  it  may  even  escape  from  the  furnace  in  the  free  state, 
that  is,  entirely  uncombined  with  oxygen.  This  free 
carbon,  deposited  from  the  volatile  hydrocarbon  in  the 
manner  indicated,  is  what  constitutes  smoke. 

The  amount  of  free  carbon  which  escapes  in  this 
way  from  the  furnace  and  appears  in  the  chimney  gases 
is  probably  considerably  less  than  is  generally  sup- 
posed, particularly  by  the  public.  A  comparatively 
small  amount  of  free  carbon  issuing  from  the  top  of 
the  chimney  is  sufficient  to  give  the  gases  a  dense 
black  appearance.  In  fact,  it  is  unlikely  if  the  amount 
of  carbon  lost  in  this  way  ever  greatly  exceeds  1  per 
cent  of  the  total  fuel.  Thus  from  the  standpoint  of 
efficiency  smoke  in  itself  is  not  such  a  serious  matter 
as  is  many  times  supposed. 

But  if  the  manner  in  which  smoke  is  formed  be 
kept  clearly  in  mind  it  will  be  plain  that  there  are 
other  effects  of  incomplete  combustion  besides  the 
visible  smoke.  These  are  CO,  free  hydrogen,  and 
unburned  hydrocarbons,  all  of  which  are  invisible 
gases,  and  which  may  reduce  furnace  efficiency  very 
seriously.  For  example,  for  each  pound  of  carbon 
burned  to  CO  instead  of  CO2,  the  loss  is  about 
10,000  heat  units.  Thus,  while  smoke  itself  may  not 
be  serious  from  the  standpoint  of  efficiency,  it  is  of 
value  as  an  index  of  bad  furnace  condition  and  poor 
efficiency. 

Of  course,  it  can  not  be  denied  that  smoke  is  open 
to  serious  objection  on  humanitarian  grounds,  on 
account  of  its  evil  effect  upon  public  health.  For  this 
reason  the  smoke  problem  has  received  a  great  amount 
of  study,  particularly  in  large  cities.  But  to  the  power 


42 


FURNACE  EFFICIENCY 


plant  owner  smoke  is  important  because  it  indicates 
serious  conditions  in  the  furnace  which  need  attention 
if  high  furnace  efficiency  is  to  be  maintained. 

The  problem  for  the  operator  of  the  boiler  furnace 
is  to  secure  complete  combustion  at  all  times  with  as 
little  excess  air  as  possible.  This  is  by  no  means  an 
easy  task,  and  one  that  calls  for  a  thorough  under- 
standing of  combustion  problems,  and  constant  atten- 
tion to  furnace  conditions.  With  a  properly  con- 
structed furnace,  a  capable  attendant  and  intelligent 
use  of  instruments  such  as  draft  gauges,  CO2  appa- 
ratus and  thermometer,  it  is  possible  to  obtain  com- 
plete combustion  with  a  fair  grade  of  soft  coal  on  as 
low  as  30  per  cent  excess  air.  The  United  States  Geo- 
logical Survey  gives  the  following  table  for  an  approx- 
imate heat  distribution  for  Illinois  coal.  The  same 
figures  will  hold  true  for  all  similar  soft  coals : 


Percentage  of  Heat. 

1 

2 

3 

1. 

2. 
3. 
4. 

5. 
6. 

Absorbed  by  boiler  
Carried    away    in    dry     chimney 
gases 

50.0 
24.0 
15.0 

4.0 
2.0 
5.0 

65.0 
16.0 
12.0 

3.5 
2.0 
1.5 

75.0 
10.0 
10.0 

3.0 
1.5 
0.5 

Radiation    and     unaccounted    for 
losses 

Moisture    formed  by   burning    of 
hydrogen                 .    .           

Evaporating  moisture  in  coal  
Incomplete  combustion  of  carbon  . 

Total  heat  .  . 

100.0 

100.0 

100.0 

TABLE  No.  T. 


Column  1  above  gives  the  heat  distribution  under 
poor  conditions,  Column  2  average  conditions  and  Col- 
umn 3  the  best  conditions  practically  attainable.  These 


FURNACE  EFFICIENCY  43 

best  conditions  are  rarely  attained  in  present  practice, 
but  they  are  not  impossible,  and  present  a  practical 
ideal  toward  which  to  strive. 

The  Observation  of  Smoke. 

The  casual  observation  of  a  smoking  chimney  may 
lead  to  very  erroneous  conclusions  as  to  the  amount 
of  smoke  coming  from  it.  A  stack  may  be  practically 
free  from  smoke  for  90  per.  cent  of  the  time,  and  if 
smoke  observations  are  made  during  the  remaining 
10  per  cent  of  the  day,  a  false  idea  is  obtained  as  to 
the  nature  of  the  combustion  in  the  plant.  A  stand- 
ard of  smoke  densities  is  required,  by  means  of  which 
various  smoking  chimneys  may  be  compared.  Also 
careful  time  observations  should  be  taken  to  determine 
the  duration  of  the  smoking,  and  the  observations 
should  be  made  at  regular  intervals  throughout  the 
day.  Only  by  such  a  method  can  reliable  results  be 
attained. 

The  standard  of  densities  which  has  the  widest 
application  in  observing  smoke  is  in  the  Ringelmann 
chart,  devised  by  Professor  Ringelmann,  of  Paris. 
This  chart  is  shown  in  Fig.  7.  Card  1  is  made  with 
black  lines  1  mm.  thick,  10  mm.  apart,  leaving  spaces 
9  mm.  square.  Card  2  has  lines  2.3  mm.  thick,  with 
spaces  7.7  mm.  square.  Card  3  has  lines  3.7  mm.  thick, 
with  spaces  6.3  mm.  square.  Card  4  has  lines  5.5  mm. 
thick,  with  spaces  4.5  mm.  square.  In  addition  to  the 
four  cards  shown  in  the  figure>  an  all-white  one  is 
sometimes  used  and  numbered  0,  while  an  all-black 
card  is  numbered  5. 

When  making  smoke  observations,  a  chart  is  pre- 
pared which  has  the  four  cards  shown  in  Fig.  7  ar- 
ranged in  a  horizontal  row.  The  all-white  card  and 
the  all-black  one  may  also  be  used.  When  this  chart 
is  observed  at  a  distance  of  about  50  feet,  the  lines  on 


44 


FURNACE  EFFICIENCY 


FURNACE  EFFICIENCY 


45 


fO 
0 


46  FURNACE  EFFICIENCY 

the  cards  can  no  longer  be  distinguished,  the  whole 
surface  assuming  a  gray  appearance.  The  heavier  the 
lines  on  the  card  the  darker  the  shade  of  gray  which 
the  surface  appears  to  be. 

In  determining  the  density  of  the  smoke,  the 
observer  glances  from  cards  to  smokestack  and  back 
again  until  he  can  pick  out  the  card  which  most  nearly 
corresponds  in  color  to  the  smoke.  If  he  should  select 
Card  No.  2  as  most  closely  corresponding  to  the  den- 
sity of  the  smoke,  then  the  latter  is  called  No.  2  smoke. 
In  the  same  way,  one  may  speak  of  No.  1  smoke,  No. 
4,  etc.  In  a  boiler  test  these  observations  should  be 
made  at  regular  intervals  throughout  the  day  and  the 
results  platted  on  a  smoke  record  chart,  the  smoke 
number  being  platted  as  an  ordinate  against  the  time 
as  abscissa.  In  this  way  the  smoke  record  for  the 
whole  day  may  be  seen  at  a  single  glance. 

Fig.  8  shows  smoke  of  densities  approximating  the 
five  cards  of  the  Ringelmann  chart.  It  will  be  noted 
that  No.  1  smoke  is  a  very  light  gray,  such  as  is  seen 
coming  from  many  chimneys  practically  all  the  time. 
Such  smoke  is  usually  allowed  by  most  city  smoke 
ordinances.  A  chimney  which  never  shows  anything 
worse  than  No.  2  smoke  would  be  considered  good, 
while  as  dense  as  No.  3  may  be  permitted  for  brief 
intervals. 

The  Prevention  of  Smoke. 

Smokeless  combustion  can  only  be  secured  by 
properly  designed  furnaces  and  eternal  vigilance  in 
operation.  The  first  requirement  is  suggested  by  the 
way  in  which  smoke  is  produced.  Since  it  is  caused 
by  insufficient  air  supply,  the  first  measure  for  its 
prevention  is  an  adequate  supply  of  air  to  the  furnace 
at  all  times.  The  measures  for  smoke  prevention  may 
be  enumerated  as  follows : 

1.     An  adequate  supply  of  air. 


FURNACE  EFFICIENCY  47 


48  Ft'KXACE  EFFICIENCY 

2.  A  temperature  throughout  the  combustion  zone 
high  enough  to  provide  for  the  complete  combustion 
of  the  volatile  gases  or  hydrocarbons. 

3.  A  slow  and  uniform  distillation  of  the  hydro- 
carbons. 

4.  An  intimate  mixture  of  gases  and  air. 

If  these  four  requirements  be  met  satisfactorily, 
then  practically  any  soft  coal  can  be  burned  without 
smoke. 

The  first  requirement  presents  no  great  difficulty, 
since  in  the  majority  of  steam  plants  far  too  great  an 
excess  of  air  is  being  used.  The  second  requirement 
is  very  largely  a  matter  of  design,  as  it  requires  a  brick 
or  tile  enclosed  combustion  chamber  of  such  size  and 
length  that  the  hydrocarbon  gases  may  be  completely 
burned  before  reaching  the  heating  surfaces  of  the 
boiler.  Whenever  a  boiler  is  set  over  a  furnace  in  such 
a  way  that  the  gases  can  come  into  contact  with  either 
shell  or  tubes  before  combustion  is  complete,  smoke 
and  poor  economy  are  almost  sure  to  result.  When 
the  flames  strike  the  relatively  cold  heating  surfaces 
they  are  chilled  below  the  ignition  temperature  of  the 
gases,  combustion  is  arrested,  and  smoke  produced. 
For  this  reason  a  tubular  boiler  set  directly  over  the 
furnace  almost  always  smokes  when  the  flames 
come  in  contact  with  the  shell.  A  brick  or  tile  roof 
must  be  provided  for  the  furnace  or  an  arch  must  be 
built  over  the  grates  so  that  the  flames  can  not  strike 
the  boiler  until  combustion  is  complete. 

The  third  requirement,  a  slow  and  uniform  distilla- 
tion of  the  gases  from  the  coal,  is  practically  impos- 
sible when  the  furnace  is  fired  by  hand.  In  order  that 
the  distillation  of  the  gases  shall  be  slow  and  uniform, 
the  fuel  must  be  fed  to  the  furnace  at  a  uniform  rate, 
and  this  is  exactly  what  hand-firing  does  not  do.  When 
a  charge  of  coal  is  thrown  into  the  fire  by  hand  there 
is  a  sudden  evolution  of  gas  while  the  coal  is  coking. 


FURNACE  EFFICIENCY  49 

The  quantity  of  gas  given  off  at  the  time  will  very 
likely  be  beyond  the  capacity  of  the  furnace  to  con- 
sume, and  imperfect  combustion  will  result.  When  the 
charge  of  coal  has  been  completely  coked,  very  much 
less  air  will  be  required  to  burn  the  fixed  carbon. 
Unless  the  supply  of  air  is  reduced  somewhat,  too 
great  an  excess  will  be  present,  with  a  consequent  loss 
in  efficiency.  Thus,  on  account  of  the  widely  varying 
demands  for  air  on  the  part  of  a  hand-fired  furnace,  it 
becomes  extremely  difficult  to  operate  such  equipment 
without  smoke.  The  mechanical  stoker  which  feeds 
the  coal  into  the  furnace  uniformly  and  steadily  makes 
smokeless  combustion  entirely  practicable. 

To  promote  the  mixing  of  the  gases  and  air,  spe- 
cial features  of  design  have  been  used,  such  as  baffle 
piers,  wingwalls,  etc.  In  the  next  chapter  these  fea- 
tures will  be  discussed,  as  well  as  the  general  design  of 
furnaces  to  promote  smokeless  combustion. 

Questions  and  Answers. 

Q.     How  is  smoke  formed? 

A.  By  the  incomplete  or  arrested  combustion  of 
the  volatile  hydrocarbons  in  the  coal. 

Q.  Is  smoke  the  only  result  of  such  imperfect 
combustion? 

A.  No,  there  is  CO  and  unconsumed  hydrocarbons 
in  the  chimney  gases  when  smoke  is  found. 

Q.  How  much  heat  is  lost,  due  to  the  formation  of 
smoke? 

A.  Much  less  than  is  generally  supposed,  probably 
not  much  more  than  1  per  cent  of  the  total  heat  of  the 
coal. 

Q.     Why,  then,  is  smoke  objectionable? 

A.  On  humanitarian  grounds,  and  because  it  is  the 
visible  sign  of  poor  conditions  in  the  furnace. 

Q.     How  is  the  density  of  smoke  estimated? 


50  FURNACE  EFFICIENCY 

A.  By  comparing  it  with  the  cards  of  the  Ring- 
gelmann  chart. 

Q.  What  is  the  first  requirement  for  smokeless 
combustion? 

A.     An  adequate  air  supply. 

Q.     Name  some  other  requirements. 

A.  A  high  temperature  in  the  combustion  zone,  a 
slow  and  uniform  distillation  of  the  gas  from  the  coal, 
and  a  proper  mixing  of  gas  and  air. 


FURNACE  EFFICIENCY  51 


CHAPTER  VI. 

In  Chapter  V  the  requirements  for  smokeless  com- 
bustion were  enumerated  and  discussed  somewhat  in 
detail.  We  shall  now  consider  some  of  the  best  types 
of  modern  furnaces,  designed  to  burn  high  volatile 
soft  coal  without  smoke,  and  note  wherein  they  meet 
the  conditions  of  smokeless  combustion  and  wherein 
they  fail  to  come  up  to  the  requirements. 

Fig.  9  shows  a  Babcock  &  Wilcox  boiler  of  220 
horse-power  rated  capacity,  described  by  Professor 
Breckenridge.  It  is  served"  with  a  Roney  stoker,  and 
equipped  with  the  usual  vertical  baffling.  Perhaps  the 
chief  feature  of  this  furnace  is  the  coking  arch,  placed 
over  the  front  end  of  the  stoker,  so  that  the  fresh  coal 
is  fed  in  directly  under  it. 

This  arch  is  of  fire  brick  and  is  sprung  between  the 
side  walls,  the  distance  between  grate  and  arch  being 
shown  in  the  figure.  This  arch  is  maintained  at  a 
high^temperature,  its  purpose  being  to  assist  in  the 
combustion  of  the  volatile  gases  as  they  are  distilled 
from  the  incoming  coal.  Experience  has  shown  that 
this  arch  should  be  kept  well  down  near  the  grates, 
to  insure  complete  combustion  of  the  gases.  Profes- 
sor Breckenridge  states  that,  with  careful  handling, 
this  furnace  could  be  operated  up  to  capacity  without 
smoke  above  No.  2  on  the  Ringelmann  chart.  At  110 
per  cent  of  capacity  and  above  it  could  not  be  operated 
without  objectionable  smoke,  except  by  an  expert 
fireman.  The  reason  why  this  furnace  smoked  when 
operated  much  above  normal  boiler  capacity  is  prob- 
ablv  not  difficult  to  see. 


FURNACE  EFFICIENCY 


FURNACE  EFFICIENCY 


53 


64  FURNACE  EFFICIENCY 

It  will  be  noted  that  the  distance  between  grates 
and  boiler  tubes  is  comparatively  short.  When  the 
boiler  was  run  at  rated  capacity  the  amount  of  coal 
burned,  and  hence  the  volume  of  gases  to  be  consumed, 
was  such  that  complete  combustion  was  secured  before 
the  gaseous  products  of  combustion  reached  the  boiler 
tubes.  Hence  combustion  was  comparatively  smoke- 
less. On  the  other  hand,  when  the  boiler  was  forced 
beyond  its  rated  capacity  the  volume  of  gases  dis- 
tilled from  the  coal  was  so  great  that  complete  com- 
bustion was  impossible  in  the  short  distance  from 
grates  to  boiler  tubes.  Hence  the  gases  were  chilled 
below  their  ignition  point  on  striking  the  compara- 
tively cold  tubes,  combustion  was  arrested  and  smoke 
produced.  The  chief  trouble  with  this  furnace  is  that 
it  does  not  have  a  combustion  space  of  sufficient  length 
to  provide  for  efficient  combustion  at  high  rates  of 
working. 

In  general,  it  may  be  said  that  the  area  and  length 
of  the  combustion  space  depend  upon  the  rate  of  com- 
bustion and  the  character  of  the  fuel.  Or  what  amounts 
to  the  same  thing,  the  combustion  space  must  be  de- 
signed with  reference  to  the  volume  of  gases  which 
must  be  consumed  per  second.  By  combustion  space 
is  meant  that  portion  of  the  furnace  which  is  sur- 
rounded by  fire  brick,  tile,  or  other  refractory  material, 
which  may  be  maintained  at  a  high  temperature.  The 
furnace  under  consideration  has  boiler  tubes  at  the 
top  of  the  furnace,  which  has  the  effect  of  greatly 
reducing  the  effective  combustion  space. 

Fig.  10  shows  a  setting  similar  to  Fig.  9,  except  that 
the  boiler  is  horizontally  baffled  instead  of  vertically. 
A  tile  roof  is  provided  for  the  furnace  by  means  of 
specially  designed  tube  tiles  placed  on  the  lower  row 
of  tubes.  Professor  Breckenridge  states  that  this  fur 
nace  could  be  operated  at  capacities  up  to  100  per  cent 
of  rating  without  smoke,  and  at  greater  capacities 


FURNACE  EFFICIENCY  55 

without  objectionable  smoke.  In  this  furnace  the  path 
of  the  gases  is  along  the  line  ABC,  and  not  until  the 
point  C  is  reached  do  the  products  of  combustion  come 
in  contact  with  the  heating  surfaces  of  the  boiler. 
Except  at  very  high  rates  of  working,  the  combustion 
space  is  sufficiently  long  to  provide  for  complete  com- 
bustion of  the  hydrocarbon  gases  before  the  point  C 
is  reached.  Thus  a  furnace  designed  in  t^iis  way  is 
much  better  from  the  standpoint  of  smokeless  com- 
bustion than  the  one  shown  in  Fig.  9. 

The  draft  required  for  this  furnace  will  probably 
be  somewhat  greater  than  for  the  one  with  the  verti- 
cal baffles  shown  in  Fig.  9.  But  if  sufficient  draft  is 
available  there  is  probably  no  doubt  that  this  furnace 
will  prove  superior  to  the  vertical  baffle  so  far  as 
smokeless  operation  is  concerned,  particularly  at  the 
higher  rates  of  working. 

Fig.  11  shows  a  210  horse-power  Heine  boiler, 
equipped  with  Green  chain-grate  stoker,  and  provided 
with  mechanically  induced  draft.  This  boiler  is  in- 
stalled in  the  Engineering  Experiment  Station  at  the 
University  of  Illinois,  and  has  been  used  by  the  sta- 
tion in  many  practical  fuel  tests.  It  will  be  noted 
that  the  furnace  is  provided  with  a  flat  combustion 
arch  over  the  front  end  of  the  grate,  and  that  a  roof 
is  supplied  by  means  of  tiles  on  the  bottom  row  of 
tubes.  Experiments  on  this  boiler  show  that  it  can 
be  operated  without  smoke  at  practically  any  rate  of 
working  and  under  almost  any  conditions  of  oper- 
ation. Ample  draft  being  available,  this  boiler  can 
be  operated  efficiently  at  very  high  overloads;  in  fact, 
Professor  Breckenridge  states  that  it  was  found  to  be 
almost  impossible  to  make  it  smoke. 

The  chief  features  of  design  which  are  respon- 
sible for  the  smokeless  operation  of  this  furnace  are : 
(1)  The  chain-grate  stoker,  which  feeds  the  fuel  into 
the  furnace  at  a  uniform  rate,  thus  giving  a  steady 


FURNACE  EFFICIENCY 


FURNACE  EFFICIENCY 


57 


evolution  of  hydrocarbon  gases,  an  important  point 
in  efficient  combustion ;  (2)  the  combustion  arch  over 
the  front  of  the  grate,  which  ignites  the  gases  as  they 
come  from  the  coal;  (3)  the  tile  roof,  which  prevents 
the  gases  from  coming  into  contact  with  the  boiler 
tubes  until  combustion  is  complete. 

Fig.  12  shows  a  smokeless  setting  designed  by  Mr. 


FIG.  12.. 


A.  Bement,  and  described  in  the  "  Proceedings  of  the 
Western  Society  of  Engineers,"  October,  1906.  This 
is  a  Babcock  &  Wilcox  boiler,  with  chain-grate  stoker. 
A  sprung  combustion  arch  is  provided  over  the  grate, 
nnd  a  tile  roof  is  placed  on  the  bottom  row  of  tubes. 
Unlike  the  setting  shown  in  Fig.  10,  this  boiler  has 
vertical  baffles,  the  path  of  the  gases  being  shown  by 


58  FURNACE  EFFICIENCY 

the  irregular  line  ABCDEF.  On  account  of  such  a 
devious  gas  path,  considerable  draft  will  be  required 
to  operate  such  a  furnace  satisfactorily,  particularly 
at  overloads.  Also  the  area  of  the  gas  path  through 
the  various  passes  must  be  proportional  with  consid- 
erable care  if  good  results  are  to  be  insured.  Such 
a  furnace,  however,  meets  practically  all  the  require- 
ments for  smokeless  operation,  and  may  be  operated 
through  a  wide  range  of  capacities  without  serious 
smoke. 

Fig.  13  shows  a  Stirling  boiler  served  with  a  chain- 
grate  stoker,  with  a  furnace  designed  for  smokeless 
combustion.  The  chief  features  of  this  furnace  are 
the  flat  ignition  arch  R,  over  the  front  of  the  grate, 
and  the  sprung  arch  P,  above  and  behind  the  ignition 
arch.  The  function  of  the  ignition  arch  is  to  assist 
in  igniting  and  coking  the  fresh  coal  as  it  is  fed  into 
the  furnace,  the  volatile  gases  being  distilled  grad- 
ually at  this  point.  The  sprung  arch  assists  in  the 
combustion  of  these  gases;  it  is  maintained  at  a  high 
temperature  and  the  gases  roll  over  the  edge  of  the 
arch  and  so  are  well  mixed  with  air,  which  is  an  impor- 
tant point  in  smokeless  combustion.  This  furnace, 
therefore,  depends  upon  these  two  arches  for  g-ood 
combustion,  which  is  effected  by  the  uniform  distilling 
action  of  the  first,  and  the  mixing  action  of  both. 

It  might  seem  at  first  sight  that  this  furnace  might 
smoke,  inasmuch  as  the  first  bank  of  tubes  is  unpro- 
tected from  the  flame  and  hot  gases.  But  experience 
has  shown  that  such  a  furnace  gives  very  good  results 
from  the  standpoint  of  smokeless  combustion,  even  at 
considerable  variations  in  the  rate  of  working.  The 
path  of  the  gases  and  products  of  combustion  is  shown 
by  the  irregular  line  ABCDEF;  it  will  be  noted  that 
the  gases  do  not  impinge  on  the  bottom  of  the  first 
bank  of  tubes,  but  turn  almost  directly  upward  from 
under  the  end  of  the  arch.  By  the  time  the  gases 


FURNACE  EFFICIENCY 


59 


FIG.  13. 


60  FURNACE  EFFICIENCY 

strike  the  tubes  combustion  is  complete,  except  pos- 
sibly at  very  high  rates  of  working. 

If  the  bottom  of  the  first  bank  of  tubes  were  cov- 
ered with  fire-clay  tile,  as  in  the  case  of  certain  other 
furnaces  already  described,  combustion  would  hardly 
be  improved  to  any  extent  because  the  gases  do  not 
strike  the  tubes  at  this  point.  On  the  contrary,  the 
efficiency  and  capacity  would  probably  be  somewhat 
reduced,  because  the  tubes  at  this  point  receive  a  con- 
siderable amount  of  heat  from  the  fire  in  the  form  of 
radiant  energy.  If  these  tubes  were  covered  with 
tile  much  of  this  radiant  energy  would  be  lost. 

All  of  the  smokeless  furnaces  discussed  thus  far 
are  in  connection  with  water-tube  boilers  and  mechan- 
ical stokers.  But  there  are  a  large  number  of  fire- 
tube  boilers  in  use  in  all  parts  of  the  country,  the  great 
majority  of  which  are  fired  by  hand.  Such  boilers  are 
usually  found  in  small  plants,  where  hand  firing  is 
cheaper  than  mechanical  stokers.  The  question  of 
smokeless  combustion  in  such  a  case  as  this  is  very 
difficult  of  solution  and  has  not  yet  been  satisfactorily 
solved. 

In  the  first  place,  hand  firing  violates  one  of  the 
chief  requirements  for  smokeless  combustion,  namely, 
a  slow  and  uniform  distillation  of  the  volatile  gases 
in  the  coal.  When  a  charge  of  coal  is  thrown  into  the 
fire  by  hand  the  gases  are  distilled  faster  than  they 
can  be  consumed  by  the  furnace,  and  smoke  results. 
Hence  smokeless  combustion  in  a  hand-fired  furnace 
under  all  conditions  of  operation  is  almost  impossible. 

In  Fig.  14  is  shown  a  perspective  view  of  a  setting 
designed  by  the  Department  of  Smoke  Inspection  of 
the  City  of  Chicago,  and  recommended  by  them  for 
use  with  the  hand-fired  horizontal  tubular  boiler.  This 
is  what  is  known  as  the  double-arch  bridge-wall  fur- 
nace, and  has  given  very  good  results  when  carefully 
operated. 


FURXACE  EFFICIENCY 


61 


62  FURNACE  EFFICIENCY 

It  will  be  noted  that  the  gases  coming  from  the 
furnace  are  divided  at  the  bridge  wall  into  two 
streams  by  means  of  a  double  arch  rising  from  the 
center  of  the  bridge  wall.  A  bulkhead  is  built  up 
around  the  shell  to  prevent  the  gases  from  escaping 
above  the  arch  and  so  coming  into  contact  with  the 
boiler  shell.  Behind  this  double  arch  there  is  a  short 
single  arch  sprung  between  the  side  walls.  This  is 
known  as  the  deflection  arch,  its  function  being  to 
deflect  the  gases  downward  after  they  leave  the  dou- 
ble arch,  and  so  prevent  them  from  impinging  on  the 
shell.  The  object  of  such  a  construction  is  to  prevent 
the  hot  gases  from  coming  into  contact  with  the  shell 
throughout  practically  its  whole  length. 

A  furnace  of  this  kind  will  probably  require  more 
draft  than  the  usual  setting  provided  for  such  a  boiler, 
on  account  of  the  devious  path  of  the  gases.  Given 
sufficient  draft,  however,  such  a  furnace  greatly  re- 
duces the  smoke  nuisance  when  the  firing  is  carefully 
done. 

Questions  and  Answers. 

Q.  In  practically  all  smokeless  furnaces,  how  is 
a  uniform  distillation  of  the  volatile  combustible  gases 
effected? 

A.  By  an  ignition  or  coking  arch  placed  over  the 
front  of  the  grate. 

Q.  How  is  a  uniform  feed  of  fuel  obtained  in  such 
a  furnace? 

A.  By  means  of  a  mechanical  stoker,  usually  some 
form  of  movable  or  traveling  grate. 

Q.  What  is  the  object  in  placing  fire  tiles  on  the 
bottom  row  of  tubes  in  a  horizontal  water-tube  boiler? 

A.  To  provide  a  tile  roof  for  the  furnace  and  so 
prevent  the  gases  from  coming  into  contact  with  the 
tubes  before  combustion  is  complete. 


FURNACE  EFFICIENCY  63 

Q.  Can  a  hand-fired  tubular  boiler  furnace  be 
operated  without  smoke? 

A.  Yes,  under  favorable  conditions  and  with  care- 
ful handling. 

Q.  What  kind  of  furnace  has  proved  most  satis- 
factory for  such  a  boiler? 

A.     The  double-arch  bridge-wall  furnace. 


64  FURNACE  EFFICIENCY 


CHAPTER  VII. 

It  will  be  evident  from  a  reading  of  the  foregoing 
chapters  that  furnace  efficiency  depends  upon  a  number 
of  conditions,  such  as  character  of  flue  gases,  draft, 
design  of  furnace  and  grate,  kind  and  condition  of  fuel, 
method  of  firing,  etc.  Many  of  these  conditions  are 
subject  to  considerable  change,  so  that  the  problem  of 
maintaining  high  furnace  efficiency  involves  a  constant 
attention  to  all  the  details  of  furnace  operation.  Fur- 
thermore, these  conditions  are  such  that  a  change 
which  would  adversely  affect  the  efficiency  might  not 
be  apparent  to  the  fireman  or  man  in  charge.  For 
example,  it  has  been  shown  that  in  general  a  relatively 
high  percentage  of  CO2  in  the  flue  gases  is  essential  to 
high  furnace  efficiency.  Also,  we  have  seen  that  a 
leaky  setting  allows  infiltration  of  air,  which  dilutes 
the  gases,  lowers  the  percentage  of  CO2  at  the  uptake 
and  decreases  efficiency.  Now,  such  a  state  of  affairs 
can  only  be  detected  by  a  flue-gas  analysis,  as  already 
explained,  and  this  takes  some  time.  The  result  is  that 
in  spite  of  flue-gas  instruments,  CO2  records,  draft 
gauges  and  thermometers,  all  of  which  are  extremely 
valuable  in  their  proper  places  and  not  for  one  moment 
to  be  underestimated,  the  fireman  still  does  not  have 
before  him  a  constant  and  reliable  index  of  what  is 
taking  place  inside  the  furnace  walls. 

From  a  proper  use  of  the  instruments  mentioned  the 
engineer  in  charge  has  learned  the  best  way  to  operate 
the  furnaces  under  certain  conditions  of  load.  But  he 
can  not  spend  all  of  his  time  in  the  furnace-room 
watching  the  fires,  so  that  for  a  part  of  the  time,  at 


FURNACE  EFFICIENCY  65 

least,  the  fireman  does  not  know  if  he  is  operating  his 
furnace  to  the  best  advantage.  If  some  instrument 
could  be  devised  which  might  be  placed  on  the  boiler 
front,  in  plain  view  of  the  fireman,  which  would  indi- 
cate at  all  times  the  efficiency  of  the  whole  steam- 
generating  process,  it  would  be  a  most  valuable  aid  in 
maintaining  proper  furnace  and  boiler  conditions. 

It  should  be  kept  clearly  in  mind  that  these  condi- 
tions can  be  determined  with  a  fair  degree  of  accuracy 
from  the  flue-gas  analysis,  draft  and  temperature  read 
ings,  and  the  evaporation  test.  But  the  difficulty  lies 
in  maintaining  conditions  favorable  to  high  efficiency 
after  they  have  been  determined.  In  the  past  it  has 
been  done  by  eternal  vigilance,  or  (more  often)  not 
done  at  all.  It  will  be  apparent,  therefore,  what  a  vast 
amount  of  time  and  trouble  would  be  saved,  and  what 
savings  in  fuel  could  be  realized  if  some  instrument 
were  available  which  would  give  at  a  glance  the  effi- 
ciency of  the  whole  steam-generating  unit. 

The  Wilsey  Fuel  Economy  Gauge  is  an  instrument 
designed  to  meet  just  these  requirements.  It  indicates 
to  the  fireman  just  what  his  combined  furnace  and 
boiler  efficiency  is  at  all  times,  and  is  practically  as 
reliable  in  its  action  as  the  steam  gauge.  A  fireman 
can  usually  be  depended  upon  to  keep  the  steam  pres- 
sure at  the  right  point,  because  he  has  the  gauge  always 
before  him  to  guide  him  in  his  work.  With  the  fuel 
economy  gauge  also  before  his  eye  he  has  a  reliable 
guide  to  keep  him  in  the  path  of  high  efficiency.  Chang- 
ing conditions  in  the  furnace  are  immediately  indicated 
on  the  economy  gauge,  and  the  fireman  can  go  to  work 
at  once  to  correct  them,  without  waiting  for  informa- 
tion from  flue-gas  apparatus  or  draft  gauge. 

One  important  distinction  is  to  be  made,  between 
the  Wilsey  Fuel  Economy  Gauge  and  all  other  instru- 
ments from  which  a  knowledge  of  furnace  conditions 
is  obtained.  These  latter  instruments  give  information 


66  FURNACE  EFFICIENCY 

in  regard  to  a  single  part  or  phase  of  the  steam-gener- 
ating process.  For  example,  the  CO2  recorder  gives 
information  in  regard  to  the  character  of  the  combus- 
tion, perhaps  the  most  important  step  in  the  entire 
operation  of  steammaking.  But  still  it  is  not  the  whole 
process,  and  the  over-all  efficiency  may  be  relatively 
low,  even  with  high  CO2.  Tubes  lined  with  scale  and 
covered  with  soot  and  dirt  may  produce  just  such  a 
result.  Similarly,  the  draft  gauge  and  the  pyrometer 
give  information  in  regard  to  a  single  phase,  respect- 
ively, of  the  steammaking  process,  not  to  the  whole. 

The  Wilsey  Fuel  Economy  Gauge  is  designed  and 
constructed  in  such  a  way  that  it  gives  information  in 
regard  to  the  combined  furnace  and  boiler  efficiency. 
That  is  to  say,  it  is  affected  not  only  by  the  efficiency 
of  heat  transfer  from  furnace  gases  to  boiler  heating 
surfaces,  but  also  by  the  combustion  conditions  in  the 
furnace.  Thus  the  instrument  is  able  to  approximate 
very  closely  the  efficiency  of  the  whole  process  of 
steammaking,  from  coal  to  steam.  In  fact,  if  corrected 
for  certain  features,  the  neglect  of  which  would  intro- 
duce error,  it  will  indicate  efficiency  with  as  great  accu- 
racy as  an  evaporative  test. 

In  considering  the  principle  upon  which  this  instru- 
ment is  based,  think  for  a  moment  of  what  takes  place 
in  a  furnace  and  boiler.  The  heat  liberated  from  the 
fuel  on  the  grate  is  carried  away  chiefly  in  two  ways : 

(1)  By  radiation  to  the  boiler  and  the  furnace  walls; 

(2)  by  heating  the  furnace  gases,  from  which  the  heat 
passes   to   the   boiler-heating   surfaces   by   convection 
and   conduction.     By   far   the   larger  amount  of  heat 
passes  to  the  furnace  gases,  and  only  a  comparatively 
small  amount  is  given  off  by  radiation. 

Now,  if  we  neglect  for  the  present  the  heat  given 
off  by  radiation  and  other  minor  items,  the  heat  liber- 
ated on  the  grate  depends  on  the  mass  of  furnace  gas, 
its  temperature  and  its  specific  heat.  This  gas  passes 


FURXACE  EFFICIENCY  67 

across  the  heating  surfaces  of  the  boiler  and  gives  up 
its  heat  to  the  water.  The  heat  remaining  in  the  gases 
after  they  leave  the  boiler  is  lost  up  the  stack.  This 
lost  heat  depends  upon  the  mass  of  gas,  its  specific 
heat  and  its  temperature  at  the  point  where  it  leaves 
the  boiler.  The  efficiency  of  the  process  is  equal  to  the 
ratio  of  the  heat  used  to  the  total  heat  liberated.  In 
expressing  this  ratio  it  is  not  necessary  to  know  the 
total  mass  of  gas  generated,  because  the  heat  in  each 
individual  unit  mass  is  the  same,  being  equal  to  the 
product  of  its  absolute  temperature  and  specific  heat. 
Let  T  =  the  absolute  temperature  of  the  furnace 
gases  in  the  combustion  chamber,  just  before  they 
strike  the  boiler  surfaces ;  let  S  =  the  specific  heat  of 
these  gases.  Similarly,  let  T1  and  S1  =  the  absolute 
temperature  and  specific  heat,  respectively,  of  the  gases 
leaving  the  boiler.  Then  the  total  heat  per  unit  mass 
of  gas  coming  from  the  furnace  is  TS;  also  the  total 
heat  per  unit  mass  of  gas  leaving  the  boiler  is  T1S1. 
The  heat  absorbed  is  TS  —  T^1,  and  the  efficiency 

rps TJS: 

of  the  process  is  -  — ~^ .     If  R  =  a  correction  to 

be   made  for  radiation,   then   the   expression   for  effi- 

XS T1S1 

ciency  becomes  E  =  \-  R. 

From  a  study  of  the  formula  it  would  appear  to 
consider  only  heat  absorption,  and  to  disregard  com- 
bustion entirely.  But  the  better  the  combustion,  the 
higher  will  be  the  value  of  T,  and  hence  the  higher 
will  E  become,  if  T1  remains  constant,  that  is,  if  the 
efficiency  of  heat  absorption  remains  the  same.  This 
is  an  important  point  and  merits  some  further  con- 
sideration. Suppose,  for  example,  that  a  boiler  and 
furnace  are  operating  under  good  conditions.  Sup- 
pose draft  and  air  supply  are  right,  and  the  gases  show 
14  per  cent  CO2.  The  combined  efficiency  under  these 


68  FURNACE  EFFICIENCY 

conditions  might  be  70  per  cent.  If  now  there  should 
be  a  considerable  falling  off  in  the  load  on  the  boiler, 
a  much  thinner  fire  will  have  to  be  carried  on  the  grate. 
But  if  the  draft  is  not  promptly  reduced  so  as  to  cut 
down  the  total  amount  of  air  passing  through  the  fur- 
nace in  proportion  to  the  reduced  rate  of  combustion, 
there  will  be  a  marked  falling  off  in  efficiency.  But 
this,  loss  in  efficiency  will  be  immediately  indicated  by 
the  economy  gauge,  because  the  furnace  gases  will 
have  their  temperature  reduced  by  the  large  excess  of 
cold  air  which  is  being  admitted  to  the  furnace. 

On  the  other  hand,  if  an  error  in  operation  be  made 
in  the  opposite  direction  and  draft  and  air  supply  are 
too  greatly  reduced,  incomplete  combustion  will  result 
with  the  formation  of  CO  and  smoke.  Again  there 
will  be  a  loss  in  efficiency,  but  this  also  will  be  indi- 
cated by  the  economy  gauge,  because  the  moment  that 
the  furnace  gases  are  bottled  up  in  the  furnace  and 
boiler  passages,  due  to  insufficient  draft,  there  will  be 
a  rise  in  the  temperature  of  the  gases  below  the 
damper.  Since  the  indication  of  the  economy  gauge 
depends  upon  T  -  -  T1,  a  rise  in  T1  reduces  that  differ- 
ence and  the  instrument  gives  a  lower  reading. 

Fig.  15  shows  a  diagram  of  the  Wilsey  Fuel  Econ- 
omy Gauge  attached  to  a  B.  &  W.  water-tube  boiler. 
It  will  be  noted  that  one  platinum  loop  is  placed  in 
the  combustion  chamber  and  the  other  in  the  uptake, 
and  that  these  loops  are  connected  to  form  two  arms 
of  a  Wheatstone  bridge.  Two  adjustable  resistances 
within  the  instrument  made  up  the  other  arms  of  the 
bridge.  Across  the  bridge  the  indicating  galvanometer 
is  connected,  with  a  series  and  a  shunt  resistance  in 
its  circuit. 

A  small  battery  current  is  passed  through  the 
bridge,  and  as  the  resistances  of  the  platinum  coils  in 
the  boiler  vary  by  reason  of  the  changing  tempera- 
tures to  which  they  are  subjected,  the  bridge  is  thrown 


FURNACE  EFFICIENCY 


70  FURNACE  EFFICIENCY 

out  of  balance  in  proportion  to  the  changing  tempera- 
ture at  the  two  points.  Now,  in  series  with  each  plati- 
num cojl  is  connected  an  external  resistance,  the  mag- 
nitude of  which  is  proportional  to  the  specific  heat  of 
the  gases  at  the  point  where  its  respective  platinum 
coil  is  located.  That  is  to  say,  the  coil  in  the  combus- 
tion chamber  has  in  series  with  it  a  resistance  propor- 
tional to  the  specific  heat  of  the  gases  at  that  point, 
and  the  coil  in  the  uptake  has  connected  to  it  a  resist- 
ance proportional  to  the  specific  heat  of  the  gases 
there. 

Thus  the  current  flowing  in  the  two  platinum  coils 
becomes  a  function  of  the  total  heat  of  the  gases  at  the 
points  where  the  coils  are  respectively  located,  and  the 
galvanometer  will  be  deflected  according  to  the  ratio 
of  the  total  heats  at  the  two  points.  The  correction 
for  the  effect  of  radiant  heat  from  the  fire  is  made  by 
adjusting  the  resistance  in  series  and  in  shunt  with 
the  galvanometer  circuit. 

It  will  be  evident  that  an  instrument  of  this  kind 
must  be  carefully  adjusted  for  each  particular  installa- 
tion. To  do  this  the  boiler  is  run  under  the  most  effi- 
cient conditions  possible,  as  shown  by  a  careful  test, 
and  then  the  resistances  in  the  four  arms  of  the  bridge 
are  adjusted  until  the  instrument  indicates  the  effi- 
ciency shown  by  the  test.  After  being  properly  ad- 
justed, the  economy  gauge  will  instantly  indicate  any 
departure  from  the  efficient  conditions  under  which 
it  was  set.  Thus  the  instrument  exercises  a  watch  on 
efficiency,  and  careful  tests  have  demonstrated  that  its 
accuracy  is  only  limited  by  the  accuracy  of  the  data 
upon  which  it  is  adjusted. 

The  coils,  Wheatstone  bridge  and  galvanometer  are 
placed  in  a  cast-iron  box  mounted  on  the  boiler  front 
in  plain  view  of  the  fireman.  The  needle  of  the  gal- 
vanometer shows  through  the  glass  front  of  the  box, 


FURNACE  EFFICIENCY 


71 


the   general   appearance   of   the   instrument   being   as 
shown  in  Fig.  16. 


FIG.  16. 


Table  No.  2  gives  the  results  of  a  number  of 
tests  run  on  a  500  horse-power  Babcock  &  Wilcox 
boiler,  under  different  conditions  of  operation. 


72 


FURXACE  EFFICIENCY 


be  noted  that  the  efficiency  as  shown  by  the  Wilsey 
Fuel  Economy  Gauge  agrees  closely  in  each  case  with 
the  results  of  the  evaporative  test. 


Efficiency  by 
Evaporation 
Per  Cent. 

Efficiency  by 
W.  F.  E.  G. 
Per  Cent. 

B.  T.  U. 
Per 
Pound. 

Per  Cent 
Ash. 

C02. 

Per  Cent 
Rated 
Capacity 
Developed 

68.9 

69.1 

•9,580 

17.2 

12.4 

158 

68.7 

69.1 

9,850 

16.7 

12.2 

130 

66.7 

67.4 

10,584 

11.8 

11.8 

141 

66.2 

67.4 

9,505 

19.8 

11.3 

146 

65.9 

66.5 

9,598 

19.5 

11.7 

147 

67.1 

66.8 

9,815 

16.6 

12.2 

153 

65  8 

64.6 

9,440 

19.5 

10  6 

127 

65.8 

64.7 

10,053 

13.8 

12.2 

156 

TABLE  No.  2. 

It  is  a  comparatively  simple  matter  to  connect  a 
recording  galvanometer  to  the  economy  gauge  and 
thus  get  a  continuous  efficiency  record  throughout  the 
twenty-four  hours  of  the  day.  Fig.  17  shows  a  chart 
from  such  a  recording  instrument,  taken  on  a  350 
horse-power  Stirling  boiler.  The  period  from  mid- 
night to  about  4  a.m.,  during  which  the  fire  was 
banked,  is  clearly  shown  on  the  chart. 

The  chief  value  of  such  an  instrument  as  the  one 
described  here  is  probably  to  be  found  not  so  much  in 
that  it  shows  the  efficiency  at  all  times,  as  that  it  shows 
instantly  any  departure  from  proper  operating  condi- 
tions. The  fireman  can  fire  by  the  economy  gauge  to 
keep  the  efficiency  high,  just  as  he  fires  by  the  steam 
gauge  to  keep  the  pressure  constant, 


FURNACE  EFFICIENCY 


73 


FIG.  17. 


74  FURNACE  EFFICIENCY 

Questions  and  Answers. 

Q.  What  is  the  function  of  the  Wilsey  Fuel  Econ- 
omy Gauge? 

A.  To  indicate  at  all  times  the  efficiency  of  the 
steam-generating  process. 

Q.     Upon  what  does  it  depend  for  its  operation? 

A.  Upon  the  difference  in  temperature  of  the  fur- 
nace gases  in  combustion  chamber  and  uptake. 

Q.     Does  all  the  heat  of  the  fuel  pass  to  the  gases? 

A.  No;  some  passes  to  boiler  and  furnace  walls 
by  radiation,  and  the  fuel-economy  gauge  must  be  cor- 
rected for  this  heat. 

Q.     How  is  the  Wilsey  instrument  constructed? 

A.  Two  platinum  coils  are  placed  in  the  furnace 
and  boiler,  one  in  the  combustion  chamber  and  the 
other  in  the  uptake.  These  coils  form  two  arms  of  a 
Wheatstone  bridge,  so  that  any  change  in  temperature 
of  the  furnace  gases  throws  the  bridge  out  of  balance. 

Q.  What  degree  of  accuracy  will  this  instrument 
show? 

A.  Its  indications  will  usually  agree  with  the 
results  of  an  evaporative  test  to  within  2  per  cent. 


FURNACE    EFFICIENCY  75 


CHAPTER  VIII. 

It  was  shown  in  a  previous  chapter  that  proper 
draft  conditions  in  furnace  and  boiler  are  of  great 
importance  in  securing  high  efficiency.  It  was  pointed 
out  that  a  certain  rather  definite  relation  must  exist 
between  the  draft  pressure  in  the  furnace  and  the 
different  passes  of  the  boiler  if  satisfactory  operating 
conditions  are  to  be  realized.  For  example:  the  loss 
in  draft  pressure  through  the  fire  bears  a  relation  to 
the  loss  through  the  boiler  which  is  very  nearly  con- 
stant for  any  particular  installation,  even  though  there 
may  be  considerable  variation  in  load.  Of  course,  this 
relation  varies  in  furnaces  and  boilers  of  different 
design,  and  must  be  determined  experimentally  and  by 
experience  for  each  particular  type.  But  after  this  rela- 
tion has  been  determined  it  furnishes  a  guide  to  effi- 
cient operating  conditions  which  is  of  considerable 
value. 

This  -fact  has  been  utilized  by  Mr.  W.  A.  Blomck 
to  produce  a  boiler  efficiency  meter,  which  gives  con- 
siderable information  in  regard  to  furnace  conditions. 
This  instrument,  as  will  be  seen  from  Fig.  18,  consists 
of  two  sensitive  draft  gauges,  mounted  in  a  suitable 
case,  one  above  the  other.  They  are  both  differential 
gauges,  the  upper  one  being  connected  between  the 
furnace  and  the  boiler  side  of  the  damper  and  the 
lower  one  between  the  furnace  and  the  outside  atmos- 
phere. Thus  one  gauge  shows  the  draft  pressure  drop 
through  the  boiler  and  the  other  the  drop  through  the 
fire.  The  tube  of  the  upper  gauge  is  filled  with  blue 
oil  and  the  lower  one  with  red  oil. 


76  FURNACE    EFFICIENCY 

Fig.  19  shows  the  complete  meter,  in  shape  to  be 
mounted  on  the  boiler  front  in  view  of  the  fireman. 
It  will  be  noted  that  each  draft  gauge  is  provided  with 
a  pointer ;  these  pointers  are  movable  and  are  set  by 
experiment  on  each  installation.  That  is,  a  'careful 
test  of  the  boiler  sho-ws  where  each  gauge  should 
stand  when  conditions  are  known  to  be  good.  Then 
the  movable  pointers  are  set  at  these  two  points,  and  it 
becomes  the  duty  oi  the  fireman  to  keep  the  oil  in  the 
gauges  as  near  them  as  possible. 


BOIL  £/P  &WG  /5-/v  c  y  Ms  r££> 
Went  Applied  for. 


FIG.    18. 


The  function  of  a  differential  draft  gauge  is  ta 
indicate  the  difference  in  pressure  between  the  two 
points  to  which  it  is  connected.  The  situation  is  sim- 
ilar in  principle  to  the  manner  in  which  a  voltmeter 
indicates  the  difference  in  electrical  pressure  between 
two  points.  Now,  as  every  engineer  knows,  the  dif- 
ference in  pressure  between  the  inside  of  the  boiler 
and  the  outside  is  due  to  the  difference  in  weight 


FURNACE    EFFICIENCY 


77 


between  the  furnace  gases  and  an  equal  volume  of  air. 
This  difference  in  weight  causes  a  pressure  which 
forces  air  through  the  furnace  and  boiler  and  up  the 
chimney.  As  the  air  and  gases  pass  through  the 
setting  from  ash  pit  to  chimney  they  encounter  a 


FIG.   19. 


certain  resistance  to  their  flow.  This  resistance 
causes  a  drop  in  draft  pressure,  just  as  the  electrical 
resistance  of  a  conductor  causes  a  drop  in  potential. 
The  magnitude  of  this  draft  pressure  loss  depends 
upon  the  resistance  encountered  in  the  boiler  passages 
and  the  rate  of  flow  of  the  gases.  That  is,  if  one  or 
both  of  the  above  quantities  should  increase,  the  pres- 
sure drop  increases,  while  if  one  or  both  decrease, 
the  drop  decreases. 

With  the  causes  of  draft  pressure  loss  kept  clearly 
in  mind,  it  is  possible  to  gain  a  fair  idea  of  the  prin- 
ciples underlying  the  operation  of  the  Blonck  effi- 
ciency meter.  Consider  first  the  lower  gauge,  which 
is  connected  between  the  furnace  and  the  outside  at- 
mosphere. This  gauge  shows  the  difference  in  draft 
pressures  between  the  two  points  to  which  it  is  con- 
nected ;  that  is,  it  shows  the  pressure  drop  through 


78  FURNACE   EFFICIENCY 

the  fire.  This  drop,  as  already  explained,  will  depend 
upon  the  resistance  of  the  fuel  bed  and  the  rate  of 
flow  of  air  through  the  fuel.  If  the  fuel  bed  is  too 
thick  or  the  fire  is  choked  with  ashes  or  slag,  there 
will  be  a  high  resistance  to  the  flow  of  air  and  conse- 
quently a  large  pressure  drop  through  the  fuel  bed. 
This  will  be  indicated  by  a  high  reading  on  the  lower 
gauge.  On  the  other  hand,  if  the  fire  is  too  thin  or 
there  are  holes  in  it,  the  resistance  to  the  flow  of  air 
will  be  reduced  to  almost  zero,  and  the  pressure  drop 
through  the  fuel  bed  will  be  greatly  reduced. 

Thus  it  follows  that  the  reading  of  the  lower  gauge 
gives  at  all  times  a  fairly  accurate  measure  of  the 
resistance  of  the  fuel  bed.  This  information,  used  in 
connection  with  the  draft  pressure  drop  through  the 
boiler  passages,  is  extremely  valuable  as  a  guide  to 
correct  furnace  conditions. 

Consider  now  the  upper  gauge  of  the  meter,  which 
is  connected  between  the  furnace  and  the  boiler  side 
of  the  damper.  This  gauge  gives  a  measure  of  the 
draft  pressure  loss  through  the  boiler,  as  distinguished 
from  the  furnace.  Now  the  resistance  to  the  flow  of 
the  furnace  gases  through  the  boiler  is  not  subject  to 
wide  and  sudden  fluctuation  as  it  is  in  the  'Case  of  the 
fuel  bed.  Of  course  this  resistance  is  subject  to  some 
change,  such,  for  example,  as  might  be  due  to  accu- 
mulations of  soot  on  the  tubes  or  in  the  flues,  defective 
baffles,  etc.,  and  the  Blonck  meter  will  give  informa- 
tion in  regard  to  just  such  conditions.  But  the  point 
to  be  kept  clearly  in  mind  here  is  that  changes  in 
draft  pressure  loss  in  the  boiler  are  chiefly  due  to 
changes  in  the  rate  of  flow  of  the  gases.  It  must  be 
remembered  that  draft  loss  depends  upon  rate  of  flow 
and  resistance,  and  since  in  normal  operation  the  lat- 
ter is  nearly  constant  or  at  most  varies  but  slowly, 
the  draft  loss  becomes  a  fairly  accurate  measure  of 
the  rate  of  flow  of  the  gases.  Thus  the  blue  upper 


FURNACE   EFFICIENCY  79 

gauge  gives  a  reading  which  is  closely  proportional 
to  the  amount  of  furnace  gases  passing  through  the 
boiler  per  unit  of  time. 

If  we  wish  to  revert  again  to  electrical  terms,  the 
upper  gauge  is  an  ammeter  which  shows  the  rate  of 
flow  through  the  boiler.  The  lower  gauge  partakes 
of  the  nature  of  a  voltmeter,  showing  the  difference  in 
draft  pressure  tending  to  force  air  through  the  fuel  bed. 

When  the  Blonck  efficiency  meter  is  to  be  applied 
to  a  steam  generating  unit  the  chief  consideration  is 
to  get  it  properly  set.  This  should  be  done  during  the 
longest  daily  period  of  average  load  on  the  boiler, 
which  will  give  as  nearly  average  load  conditions  as  it 
is  possible  to  get.  All  operating  conditions,  such  as 
thickness  of  fire,  position  of  damper,  method  of  firing, 
frequency  of  cleaning  fires,  etc.,  should  be  carefully 
regulated  to  give  the  most  efficient  operating  condi- 
tions obtainable.  In  determining  these  conditions  the 
hand-  flue  gas  instrument  will  be  found  to  give  much 
valuable  information.  When  the  desired  conditions 
have  been  obtained  the  movable  pointers  shown  in 
Fig.  19  are  set  to  the  points  where  the  oil  stands  in  the 
two  gauges.  It  is  now  the  duty  of  the  furnace  oper- 
ator to  keep  the  gauges  as  nearly  as  possible  at  these 
two  fixed  points.  The  manner  in  which  the  meter  is 
connected  to  the  boiler  and  the  location  of  the  draft 
tubes  is  shown  in  Fig.  20. 

The  action  of  the  meter  under  different  conditions 
of  operation  is  as  follows:  Suppose  that  the  fire 
becomes  too  thin,  or  holes  burn  in  it,  or  it  burns  short 
at  the  back.  This  means  that  the  draft  loss  through 
the  fire  will  be  small,  and  the  red  gauge  will  give  a 
smaller  reading  than  it  should.  But  the  large  volume 
of  air  passing  through  the  furnace  and  boiler  will 
cause  an  increase  in  draft  pressure  drop  between  fur- 
nace and  uptake.  This  will  be  indicated  by  a  larger 
reading  on  the  blue  gauge.  Such  a  condition  as  this  is 


80 


FURNACE    EFFICIENCY 


shown  in  Fig.  21,  Example  No.  2  The  relative  position 
of  the  two  gauges  for  normal  operation  is  shown  in 
Example  No.  1. 

When  the  fire  is  too  thick,  or  choked  with  ashes 
and  slag,  there  will  be  a  greater  drop  than  normal 
through  the  fire,  while  on  account  of  the  reduced  air 
supply  there  will  be  less  drop  through  the  boiler. 


Ai  FUBNACC?  CONNK.TION. 
D. 


CONNECTIONS     OF     BOILER     EFFICIENCY     MFTER     TO 
WATER    TUBE    BOILER. 


This  condition  is  shown  in  Example  No.  3.  It  will 
be  noted  that  in  the  two  'Cases  considered  thus  far  the 
two  gauges  moved  in  opposite  directions  from  their 
normal  points.  This  wrill  be  the  case  when  the  load 
remains  practically  constant,  and  the  only  change  is 
in  the  condition  of  the  fire. 

In  Example  No.  4  is  shown  the  indications  of  the 
meter  when  the  boiler  is  running  with  an  overload. 


FURNACE    EFFICIENCY 


81 


In  this  case  comparatively  thick  fuel  bed  must  be 
carried  in  order  to  supply  the  necessary  rate  of  com- 
bustion. But  the  damper  must  now  be  wide  open  so 
as  to  furnish  enough  draft  to  force  the  required 
amount  of  air  through  the  thick  fuel  bed.  The  result 
is  an  increase  in  the  pressure  drop  through  the  fire, 


/,  Normal  operation  of  boiter\ 


2,  Too  much  oir,£jel  bed  too  thin  or  holes' 

3,  Too  little  air,  fiiel  bed  hothictfor 

ChofC<sdbystacj\ 

,  Boiler  running  with  overload-^ 


5,  Boifer  running  with  under  food  •* 


FIB.    21. 

DIAGRAM    OF   BOILER    EFFICIENCY    METER    AND    PRINCIPAL 
INDICATIONS?    OF    INSTRUMENT. 

because  both  resistance  and  rate  of  air  flow  have 
increased.  This  gives  an  increased  reading  on  the  red 
gauge,  the  oil  moving  to  the  right  as  shown.  But 
since  more  air  is  flowing  through  the  fire  than  before, 
the  pressure  drop  through  the  boiler  increases.  This 
gives  a  larger  reading  on  the  blue  gauge,  the  oil  mov- 
ing to  the  right  as  shown.  The  conditions  indicated 
by  such  a  reading  of  the  gauge  (see  No.  4)  are  satis- 
factory, because  the  ratio  between  furnace  drop  and 
boiler  drop  has  not  been  changed  to  any  extent. 


82 


FURNACE   EFFICIENCY 


Example  No.  5  shows  the  indication  of  the  meter 
under  light  load.  In  this  case  the  fire  is  thin  and  the 
pressure  drop  through  it  is  small,  which  gives  a 
reduced  reading  on  the  red  gauge.  But  the  stack 


Boit.ee  E:F&'ct£Nc  Y  M&r&a  . 

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FIG.    22. 
TYPICAL,    READINGS    FOR    A   WATER    TUBE    BOIER. 

draft  has  been  reduced  by  partially  closing  the  dam- 
per, so  that  less  air  is  being  forced  through  the  fire  in 
proportion  to  the  reduced  rate  of  combustion.  This 
gives  less  pressure  drop  through  the  boiler  and  a 
reduced  reading  on  the  blue  gauge,  as  shown.  Here 
again  the  ratio  of  the  two  drops  remains  practically 
constant?  so  that  conditions  are  about  as  they  should 
be  for  this  particular  load. 

The  manner  in  which  the  indications  of  the  meter 
show  the  conditions  within  the  furnace  and  boiler  is 
shown  in  Fig.  22.  The  upper  curve  in  the  figure  shows 


FURNACE   EFFICIENCY 


83 


the  percentage  of  CO2,  which  runs  from  a  minimum 
of  6  per  cent  to  a  maximum  of  11.5  per  cent.  The 
dotted  curves  show  the  reading  of  the  upper  and  lower 
gauges,  respectively,  in  hundredths  of  an  inch.  At  the 
beginning  of  the  test  the  CO2  was  6  per  cent,  the 
upper  gauge  read  80  and  the  lower  one  22.  Now  6 
per  cent  CO2  indicates  too  much  air.  The  fire  was 
therefore  gradually  thickened,  which  increased  the 


BOILER         EFFICIENCY        METER 

MNtt  -BOILER     575    M  p  CAPACITY,  GKECN  CHAIN    &RATC.   RUMNINC     FULULOAD 
TEST  OCTOBER     IO,    1912 


FIG.    23. 

RESULTS    OF    TEST    ON    BOILER    WITH    CHAIN    GRATE 
SHOWING   EFFECT   OF  OPEN   ASH   DOOR. 

pressure  drop  through  the  fire,  but  decreased  the  air 
supply.  Therefore  the  lower  gauge  read  more,  the 
upper  one  less,  and  the  CO2  increased.  This  was 
continued  until  11.5  per  cent  CO2  was  reached,  when 
the  lower  gauge  read  35  and  the  upper  one  70.  A 
further  increase  in  thickness  of  fire  carried  air  reduc- 
tion too  far,  which  resulted  in  the  formation  of  smoke 


84  FURNACE    EFFICIENCY 

and  CO,  with  less  CO2.  Therefore  the  movable 
pointers  on  the  efficiency  meter  were  set  at  70  for  the 
upper  gauge  and  35  for  the  lower  one. 

Fig.  23  shows  the  result  of  a  test  of  a  375  horse- 
power Stirling  boiler,  with  Green  chain  grate  stoker. 
The  chief  point  of  interest  in  these  curves  is  the  sud- 
den drop  in  CO2  at  11 :05  a.m.  It  will  be  noted  that 
the  reading  of  the  upper  gauge  of  the  meter  increased 
at  this  time,  while  the  lower  one  decreased.  This 
expansion  o»f  the  distance  between  the  two  gauges  is 
an  indication  of  inefficient  conditions,  as  we  have 
already  seen,  and  thus  agrees  with  the  low  CO2  noted 
at  that  time.  This  condition  was  caused  by  the  open- 
ing of  an  ash  clean-out  door  in  the  basement,  which 
resulted  in  excess  air  being  admitted  to  the  furnace. 
It  will  be  seen  from  this  figure  that  whenever  the 
readings  of  the  two  gauges  approach  each  other  the 
CO2  is  high  and  combustion  conditions  are  good,  and 
that  when  the  distance  between  the  gauges  increases 
the  opposite  results  are  noticed.  This  is  true  until 
the  position  of  normal  setting  is  reached. 

Fig.  24  shows  the  results  of  a  test  on  a  375  horse- 
power Wickes  boiler,  served  with  a  Murphy  stoker. 
These  curves  show  the  behavior  of  the  meter  during 
period's  of  excess  air  and  lack  of  air,  the  shaded  por- 
tions showing  the  nature  of  the  air  supply.  The  nor- 
mal setting  of  the  gauges  is  77  for  the  upper  one  and 
18  for  the  lower  one.  When  the  difference  is  greater 
than  this  there  is  excess  air  and  low  CO2,  as  at  12  :17 
p.m.,  for  example.  When  the  difference  between  the 
two  gauges  is  less  than  normal  there  is  fair  CO2,  but 
reduced  steaming  capacity,  as  shown  at  11:52  a.m. 
This  shows  that  CO2  is  not  always  a  safe  guide  to 
high  efficiency.  When  the  air  supply  is  unduly  re- 
stricted the  CO2  may  be  fairly  high,  but  there  will  also 
be  CO,  smoke,  reduced  capacity,  and  reduced  effi- 
ciency. This  condition  is  plainly  shown  by  the  meter, 


FURNACE   EFFICIENCY 


85 


the  difference  between  the  two  gauges  being  less  than 
normal. 

Fig.  25  shows  results  taken  from  a  test  of  a  B.  & 
W.  boiler,  with  B.  &  W.  chain  grate  stoker.  The 
effect  upon  the  efficiency  meter  of  length  of  fire  and 


BOILER      EFFICIENCY     METER 

PMV      STOKCIt     KUNNIMq  FULL     LOAD 
TEST     JANUARY      9,    191.3 


FIG.    24. 

TEST    SHOWING    RELATION    BETWEEN    AIR    STTPPY    AND 
CO,  IN    FLUE   GAS. 

thickness  of  fuel  bed  is  clearly  shown.  The  test  was 
begun  with  a  9-inch  fire,  the  upper  gauge  reading 
about  80  and  the  lower  one  60.  As  the  test  continued 
the  distance  between  the  gauge  readings  increased, 
and  the  CO2  dropped,  indicating  excess  air  and  reduced 
efficiency. 

At  about  11:10  a.  m.  the  thickness  of  the  fire  was 
increased  to  10J4  inches,  but  the  results  did  not  be- 
come noticeable  until  about  11 :35  a.m.,  because  of  the 


86 


E   S 

to 

09 
H 
^ 


FURNACE    EFFICIENCY  87 

slow  travel  of  the  grate.  At  this  point  it  will  be  seen 
that  the  curves  representing  gauge  readings  crossed 
each  other.  That  is,  the  draft  pressure  drop  through 
the  fire  became  greater  than  that  through  the  boiler. 
This  indicates  too  thick  a  fire,  insufficient  air  passing 
through  the  boiler,  and  hence  reduced  steaming  capac- 
ity, even  though  the  CO2  is  fairly  high. 

At  12:05  p.m.  the  thickness  of  fire  was  reduced  to 
8  inches,  with  the  result  that  the  gauge  reading  curves 
recrossed  each  other,  indicating  that  conditions  were 
about  correct  again.  A  study  of  these  curves  will 
show  that  thickness  of  fire  and"  length  of  fire,  whether 
short  or  long,  have  an  immediate  effect  upon  the  effi- 
ciency meter. 

Fig.  26  shows  the  results  of  a  test  on  the  same  B.  & 
W.  boiler,  the  object  being  to  show  the  effect  upon 
the  efficiency  meter  of  different  rates  of  working,  as 
shown  by  a  General  Electric  Steam  Flow  Meter.  The 
upper  curve  shows  the  instantaneous  flow  meter  read- 
ings, while  the  average  is  shown  by  the  dotted  line. 
It  will  be  seen  that  the  curve  representing  average 
rate  of  evaporation  is  practically  parallel  to  the  curves 
showing  the  readings  of  the  meter  gauges.  Thus  the 
relative  distances  of  both  gauges  from  their  normal 
points,  indicated  by  the  fixed  arrows  or  pointers,  are 
a  measure  of  the  lead  carried  by  the  boiler.  If  both 
gauges  go  above  this  normal  point,  there  is  an  over- 
load ;  if  below,  there  is  an  underload.  (See  Fig.  20.) 

It  will  be  evident  from  the  curves  that  have  been 
presented  herewith  that  the  Blonck  Efficiency  Meter 
"can  be  relied  upon  to  give  much  valuable  information 
in  regard  to  conditions  in  the  furnace.  Also,  it  gives 
this  information  almost  instantly,  so  that  faulty  con- 
ditions can  be  corrected  before  serious  loss  can  occur. 
If  its  indications  are  intelligently  made  use  of,  there 
can  be  no  doubt  but  that  the  Blonck  meter  will 
greatly  assist  in  maintaining  high  furnace  efficiency. 


FURNACE    EFFICIENCY  89 

Questions  and  Aswers. 

Q.  What  are  the  essential  parts  of  the  Blonck 
Boiler  Efficiency  Meter? 

A.     It  consists  of  two  differential  draft  gauges. 

Q.  How  are  these  gauges  connected  in  the  fur- 
nace and  boiler? 

A.  One  is  connected  between  furnace  and  outside 
atmosphere,  and  the  other  between  furnace  and  boiler 
side  of  damper. 

Q.     What  do  these  gauges  show? 

A.  One  shows  draft  pressure  loss  through  the  fire 
and  the  other  the  loss  through  the  boiler. 

Q.     How  can  these  readings  indicate  efficiency? 

A.  They  show  the  relation  between  furnace  loss 
and  boiler  loss,  which  have  a  nearly  constant  relation 
when  efficient  conditions  are  maintained. 


90  FURNACE   EFFICIENCY 


CHAFER  IX. 
The  Chain  Grate  Stoker. 

It  was  shown  in  a  previous  chapter  that  one  of  the 
most  essential  conditions  for  efficient  and  smokeless 
combustion  is  a  slow  and  uniform  distillation  of  the 
volatile  gases  from  the  coal.  This  requires  a  gradual 
and  continuous  feeding  of  the  fuel  into  the  furnace, 
so  that  the  evolution  of  the  gas  may  be  maintained  at 
a  uniform  rate. 

This  principle  has  been  recognized  by  engineers  for 
some  time,  and  has  been  kept  prominently  in  mind  in 
the  design  of  most  mechanical  stoking  devices.  It  is 
known  as  the  principle  of  progressive  combustion,  the 
fuel  being  carried  gradually  forward  into  the  furnace 
as  the  combustion  progresses.  Even  before  the  days 
of  mechanical  stokers  when  all  boiler  furnaces  were 
fired  by  hand,  this  principle  was  applied  to  a  limited 
extent.  It  consisted  in  charging  the  green  fuel  onto  a 
dead  plate  just  inside  the  furnace  door,  where  the 
volatile  gas  was  driven  off.  When  the  coal  had  be- 
come fairly  well  coked  it  was  then  pushed  back  on  the 
grate  where  the  combustion  of  the  fixed  carbon  took 
place.  This  method  of  firing  is  still  made  use  of  in 
many  hand-fired  furnaces,  but  it  is,  of  course,  open  to 
the  serious  objection  that  large  quantities  of  cold  air 
enter  the  furnace  while  the  fire-door  is  open,  and  thus 
the  efficiency  is  reduced.  This  same  objection  applies 
to  a  greater  or  less  extent  to  any  method  of  firing  by 
hand. 

The  chain  grate  stoker  is  a  device  which  provides 
for  this  method  of  progressive  combustion,  while  at 


FURNACE    EFFICIENCY 


91 


the  same  time  excluding  all  unnecessary  air  from  the 
furnace.  The  first  stoker  of  this  kind  was  designed  in 
England,  but  it  is  now  used  very  largely  in  this  coun- 
try, American  designers  and  engineers  having  added 
many  improvements  over  the  original  design,  by  which 
it  is  better  adapted  to  American  coals.  It  consists  of  a 
moving  endless  chain  mounted  on  a  frame,  the  fuel 
being  carried  forward  on  the  chain.  This  method  of 
feeding  the  coal  into  the  furnace  is  an  almost  ideal 
application  of  the  principle  of  progressive  combustion. 
The  volatile  gases  are  first  driven  off  by  the  heat 
radiated  from  the  incandescent  parts  of  the  furnace. 
Then  the  fixed  carbon  is  completely  consumed,  and 
when  the  chain  reaches  the  end  of  its  travel  the  asnes 
are  dumped  and  the  chain  kept  clean  and  free  from 
ash  or  clinker. 


FIG.    27. 
CHAIN    GRATE    STOKER. 


A  good  idea  of  the  construction  and  general  ap- 
pearance of  the  chain  grate  stoker  may  be  obtained 
from  Fig.  27.  It  will  be  noted  that  the  whole  device  is 


92  FURNACE    EFFICIENCY 

mounted  on  rollers  running  on  a  track,  thus  making  it 
comparatively  easy  to  remove  the  stoker  from  under 
the  boiler  in  case  extensive  repairs  are  required.  Small 
repairs  like  the  replacing  of  broken  links,  can  be  made 
without  removing  the  stoker  and  usually  without  even 
stopping  it.  Fig.  28  shows  a  front  view  of  the  stoker 
with  the  chain  removed,  and  Fig.  29  a  rear  view. 


FIG.    28. 
FRONT  VIEW   OF  STOKER   WITH   CHAIN    REMOVED. 


In  the  design  of  a  machine  of  this  kind  there  are  a 
number  of  important  points  to  be  considered  if  it  is  to 
give  satisfaction  under  severe  conditions  of  operation. 
In  the  first  place,  the  frame  upon  which  the  chain  is 
mounted  must  not  be  exposed  too  directly  to  the  heat 
of  the  furnace,  for  it  would  warp  and  crack  and  would 
soon  be  destroyed.  A  glance  at  Fig.  27  will  show  that 
in  the  modern  chain-grate  stoker  the  side  girders  of 
the  frame  are  removed  a  considerable  distance  from 
the  fire,  and  they  are  also  provided  with  large  air 
spaces.  This  keeps  the  side  girders  'Cool  and  assists 
in  providing  a  uniform  supply  of  air  to  the  underside 
of  the  chain,  that  is,  beneath  the  fuel  bed. 


FURNACE   EFFICIENCY  93 

When  such  a  stoker  is  subjected  to  hard  and  con- 
tinuous service  it  is  to  be  expected  that  a  link  will 
occasionally  break  or  burn  out  and  will  have  to  be 
replaced  by  a  new  one.  In  the  early  designs  the  links 
were  simply  strung  on  a  round  rod,  holes  being  pro- 
vided in  the  links  to  receive  the  rod.  This  made  the 
removal  of  a  wornout  link  a  rather  troublesome  job, 
since  it  could  not  be  taken  out  without  disturbing  all 
the  other  links  between  it  and  the  end  of  the  rod.  This 
involved  stopping  the  stoker  and  possibly  a  shut-down 
of  the  boiler,  for  a  short  time  at  least.  Fig.  30  shows 
the  links  used  on  the  Green  chain-grate  stoker,  by 
means  of  which  this  trouble  is  avoided.  The  links 
have  slotted  openings  and  the  connecting  bar  upon 


FIG.    29. 
REAR  VIEW  OF  STOKER   WITH   CHAIN   REMOVED. 

which  they  are  mounted  is  oval  in  cross  section.  In  a 
certain  position  this  connecting  bar  will  slip  into  the 
slot  in  a  link,  but  when  the  bar  is  turned  slightly  it 
is  locked  in  position  and  can  not  be  removed.  The 


FURNACE    EFFICIENCY 


PIG.    30. 
LINKS  FOR  CHAIN. 


FURNACE    EFFICIENCY  95 

binder  links  are  provided  with  holes  instead  of  slots, 
and  are  placed  one  at  each  end  of  the  connecting  bars. 
Cotter  pins  are  then  applied  to  hold  the  binder  links 
in  place ;  these  cotters  and  end  links  are  shown  clearly 
in  Fig.  27. 

With  such  an  arrangement,  when  a  link  is  to  be 
removed  it  is  only  necessary  to  remove  cotter  pins 
and  binder  link,  turn  the  connecting  bar  slightly  and 
lift  the  link  out.  .  This  operation  can  be  done  quickly, 
it  being  unnecessary  in  many  cases  to  even  stop  the 
stoker,  as  already  mentioned. 

In  the  Green  grate,  in  sizes  exceeding  7  feet  6  inches 
in  width,  the  chain  surface  is  ''double  web."  That  is, 
the  chain  surface  consists  of  two  continuous  sections, 
the  connecting  bars  extending  only  half  way  across 
the  total  width  of  chain.  This  requires  binder  links  in 
the  middle  of  the  chain,  a  special  design  being  used 
which  does  not  require  the  removal  of  the  link  in 
order  to  turn  the  connecting  bar  when  some  inside  link 
is  to  be  removed. 


FIG.    31. 
TENSION    ADJUSTING    DEVICE. 


It  is  also  very  essential  that  chain  tension  be  ad- 
justable without  removing  the  stoker  from  the  furnace 
space.  The  method  by  which  this  is  done  may  be  seen 
from  Fig.  29,  and  also  more  in  detail  from  Fig,  31. 


96  FURNACE    EFFICIENCY 

The  adjusting   screws   are   accessible   from   the   rear 
while  the  stoker  is  in  place. 

The  stoker  is  driven  from  an  eccentric  on  a  line 
shaft,  placed  either  overhead  or  below  the  floor.  The 
driving  mechanism  is  shown  from  two  different  points 
of  view  in  Figs.  32  and  33.  It  will  be  seen  to  consist 


FIG.    32. 
DRIVING  MECHANISM. 

of  a  ratchet  operated  by  the  rod  from  the  overhead 
(in  this  case)  eccentric ;  cast-steel  pawls  and  cast-steel 
spur  gear  train.  The  whole  is  carried  on  an  inde- 
pendent frame,  bolted  to  the  stoker  frame.  A  study  of 
Figs.  32  and  33  in  connection  with  Fig.  27  will  make 
plain  just  how  the  stoker  is  driven. 

Fig.  34  shows  the  design  of  the  sprockets  which 
carry  the  chain.  They  are  mounted  on  the  front  and 
rear  sprocket  shafts,  Fig.  28  plainly  showing  the  ar- 


FURNACE  EFFICIENCY  97 

rangement.  It  will  be  noted  that  these  sprockets  are 
made  scalloped  between  the  teeth,  the  purpose  being 
to  insure  the  proper  seating  of  the  drive  links  of  the 
chain  upon  the  sprockets.  This  proper  seating  might 
not  occur  if  the  chain  should  reach  the  front  sprockets 
covered  with  ashes  accumulated  during  its  return 
travel  from  rear  to  front  sprocket  shaft. 

The  thickness  of  full  bed  which  the  stoker  receives 
is  controlled  by  a  regulating  feed  gate.  It  is  supported 
from  a  square  shaft  shown  plainly  in  Fig.  28,  and 


FIG.    33. 
DRIVING    MECHANISM. 


moves  up  and  down  between  vertical  guides.  The 
square  shaft  carries  a  sector  on  one  end  engaging 
a  worm  on  the  opposite  side  of  the  frame  from  the 
driving  mechanism.  In  this  way  the  gate  may  be 


98  FURNACE   EFFICIENCY 

readily  raised  or  lowered  to  vary  the  thickness  of  the 
fire.  A  lining  of  fire  brick  is  used  to  protect  the  metal 
of  the  gate  from  the  heat  of  the  furnace.  A  frequient 
source  of  trouble  with  the  feed  gate  has  been  the  ten- 
dency of  the  fire  to  eat  back  into  the  coal  hopper  and 


FIG.    34. 
SPROCKET. 


thus  in  time  damage  and  destroy  the  gate.  This 
trouble  is  now  prevented  in  the  Green  stoker  by  pla- 
cing removable  shields  on  the  gate  in  such  a  manner 
as  to  maintain  a  ventilated  air  space  between  the 
shield  and  the  outside  of  the  gate,  thus  protecting  the 
latter  from  the  heat.  The  shields  extend  below  the 
bottom  o>f  the  tile  lining  to  protect  it  from  injury,  and 
thus  the  shields  determine  the  thickness  of  the  fuel 
bed.  Details  of  the  gate  constraction  are  shown  in 
Fig.  35. 

An  important  point  in  connection  with  the  opera- 
tion of  a  chain-grate  stoker  is  the  proper  ignition  of 
the  fuel  as  it  enters  the  furnace.  Perhaps  the  most 
successful  method  at  the  present  time  is  a  flat  ignition 
arch  placed  over  the  front  of  the  grate.  This  arch  re- 


FURXACE    EFFICIENCY 


09 


ceives  heat  from  the  fire  and  reflects  it  down  on  the 
incoming  coal,  thus  raising  the  temperature  until  the 
volatile  gases  are  driven  off  and  the  coke  is  ignited.  A 
flat  arch  of  this  kind  is  much  easier  to  build  and  main- 
tain than  a  sprung  arch,  and  being  equally  distant  from 
the  fuel  all  the  way  across  the  furnace  it  gives  a  uni- 
form igniting  effect. 

Figs.  36  and  37  show  the  construction  and  method 
of  support  of  a  flat  ignition  arch  designed  and  patented 
by  the  Green  Engineering  Company.  Two  channels 
comprise  the  main  supporting  frame ;  between  these 
channels  a  number  of  I-beams  are  run,  the  latter  sup- 
porting the  special  fire  tiles  as  shown  in  Fig.  36.  This 


FIG.    35. 
DETAILS  OF  REGULATING    FEED  GRATE. 

method  of  construction  removes  all  side  thrust  upon 
the  side  walls  cf  the  boiler  setting,  which  is  impossible 
with  any  form  of  sprung  arch. 

In  connection  with  the  chain-grate  stoker  the  water 
back  is  an  important  feature.    Fig.  39  shows  a  pressure 


i(»  FURNACE   EFFICIENCY 

water  back  in  position  in  the  furnace.  It  will  be  seen 
to  consist  of  two  lengths  of  pipe  connected  together 
at  one  end,  and  at  the  other  connected  to  the  water 
space  of  the  boiler.  Thus  the  water  back  becomes  a 


FIG.    36 
METHOD    OF    SUPPORTING    FIRE    TILE    IN    IGNITION    ARCH. 


part  of  the  water  circulation  system  of  the  boiler, 
water  flowing  through  it  at  all  times.  The  water  back 
is  placed  just  above  the  chain  at  the  rear  end,  and 
under  the  overhang  of  the  bridge  wall.  In  this  position 
it  protects  the  bridge  wall  from  the  excessive  heat  of 
the  furnace,  and  also  adds  to  the  heating  surface  of  the 
boiler.  It  is  not  improbable  that  as  much  as  one 
boiler  horse-power  is  generated  per  square  foot  of 
water-back  surface. 

In  order  to  get  high  furnace  efficiency  with  a  chain- 
grate  stoker  it  is  necessary  to  prevent  the  infiltration 
of  excess  air  at  all  points,  as  indeed  it  is  with  any  form 
of  furnace.  Leakage  is  very  likely  to  occur  at  the  end 
of  the  grate  between  the  chain  and  the  overhanging' 
bridge  wall.  The  water  back  helps  to  close  up  this 
space,  but  there  must,  of  course,  be  enough  free  space 
to  allow  for  the  discharge  of  the  ashes.  In  order  to 


FURNACE    EFFICIENCY ;  '  1'H 

make  sure  that  no  leakage  of  air  will  occur  at  this 
point  a  damper  is  plaiced  below  in  such  a  manner  as 
to  effectually  prevent  the  entrance  of  air.  This 
damper  is  shown  in  the  setting  elevation,  Fig.  38. 

The  chain-grate  stoker  described  thus  far  is  de- 
signed for  use  with  free-burning,  high-volatile  coal. 
When  low-volatile  coals  are  to  be  used  a  somewhat 
different  design  is  required.  Fig.  40  shows  the  Green 
L  Type  Stoker,  designed  for  this  purpose.  The  chief 
difference  between  this  stoker  and  the  type  already 
described  is  the  inclined  plate  at  the  front,  down  which 
the  coal  is  made  to  slide  by  a  slight  agitation  of  the 
plate.  This  serves  to  break  up  the  coal  and  deliver  it 
to  the  chain  in  a  fragmentary  condition.  The  tendency 
of  this  ccal  is  to  cake  as  the  volatile  is  driven  off  and 
the  agitation  of  the  plate  sie'rves  to  prevent  its  forming 
in  a  more  or  less  solid  mass. 

The  chain-grate  stoker  in  the  forms  described  here 
has  a  wide  application  in  steam  boiler  pratice.  With 


FIG.    37. 
METHOD  OF  SUPPORTING  IGNITION  ARCH. 

a  properly  constructed  furnace  it  can  be  operated  with- 
out smoke  and  with  high  economy  with  very  low-grade 
coal.  The  charges  for  stoker  and  furnace  maintenance 
and  repair  are  probably  as  low  as  for  any  other  me- 


104 


FURNACE   EFFICIENCY 


chanical  stoker  on  the  market,  and  lower  than  many. 
It  adapts  itself  well  to  heavy  overload  conditions,  with 
very  little  loss  in  efficiency.  The  increasing  number 


FIG.    40. 
CHAIN   GRATE    STOKER    FOR   CODING   COALS. 


of  these  stokers  in  use  indicates  that  it  meets  satis- 
factorily a  wide  range  of  conditions  in  steam-boiler 
practice. 

Questions  and  Answers. 

Q.  What  is  one  of  the  most  important  require- 
ments for  smokeless  combustion? 

A.  A  uniform  distillation  of  the  volatile  gases 
from  the  coal. 

Q.     How  is  this  best  effected? 

A.  By  a  uniform  rate  of  feed  of  the  fuel  to  the 
furnace. 

Q.     Name  one  device  designe.d  for  this  purpose? 

A.     The  chain-grate  stoker. 

Q.     What'  is  the  essential  part  of  the  stoker? 


FURNACE    EFFICIENCY  105 

A.  A  moving  endless  chain  which  carries  the  fuel 
into  the  furnace. 

Q.     How  is  this  chain  moved? 

A.  Power  is  supplied  from  an  eccentric  on  a  line 
shaft;  the  rod  from  the  eccentric  operates  a  ratchet 
and  pawl  which  drive  the  stoker  by  means  of  a  train 
of  spur  gears. 

Q.     Can  the  rate  of  travel  of  the  stoker  be  changed? 

A.  Yes,  the  point  where  the  eccentric  rod  is  fas- 
tened to  the  ratchet  is  adjustable,  which  varies  the 
travel  of  the  pawl. 

Q.  How  is  the  thickness  of  the  fuel  bed  con- 
trolled? 

A.  By  an  adjustable  gate  at  the  front  of  the  sto- 
ker. 

Q.     What  is  a  water  back? 

A.  A  pipe  placed  at  the  back  end  of  the  grate  in 
front  of  the  bridge  wall,  through  which  water  circu- 
lates. 

Q.     What  is  its  purpose? 

A.  To  protect  the  bridge  wall  and  assist  in  sealing 
the  rear  of  the  furnace. 

Q.     What  is  an  ignition  arch? 

A.  A  flat  arch  in  the  front  of  the  furnace  which 
helps  to  ignite  the  incoming  coal. 


106  FURNACE    EFFICIENCY 


CHAPTER  X. 
The  Murphy  Automatic  Furnace. 

The  chain-grate  stoker  discussed  in  the  previous 
chapter  is  perhaps  the  best  known  example  of  the  front 
feed  principle  in  automatic  stoking  devices.  Another 
well-known  and  widely  used  method  is  that  of  the 
"side  feed/'  in  which  the  fuel  is  fed  into  the  furnace 
from  two  magazines,  one  on  either  side  of  the  setting. 
Perhaps  the  best  known  example  of  the  side-feed  prin- 
ciple in  automatic  stokers  is  the  Murphy  furnace. 

A  good  idea  of  this  furnace  may  be  obtained  from 
Fig.  41,  which  shows  a  transverse  section  viewed  from 
the  rear  end.  A  similar  view  is  shown  in  Fig.  42,  in 
which  more  of  the  details  of  construction  may  be  seen. 
This  stoker  will  be  seen  to  consist  essentially  of  two 
inclined  grates,  one  on  each  side  of  the  furnace,  the 
upper  end  being  at  the  side  and  the  lower  end  near  the 
center.  These  grates  are  made  up  of  two  different 
kinds  of  bars  arranged  alternately.  In.  Fig.  43  is  shown 
the  general  appearance  and  design  of  these  grate  bars, 
one  of  which  is  stationary  and  the  other  movable.  The 
movable  bars  are  pivoted  at  their  upper  ends,  and  are 
given  a  rocking  motion  at  their  lower  ends  by  means 
of  a  rocker  bar.  This  gives  them  a  motion  alternately 
above  and  below  the  stationary  bars  and  in  this  way 
the  fuel  bed  is  kept  broken  up  and  the  movement  of  the 
coal  down  the  incline  is  facilitated.  It  will  be  noted 
from  Fig.  43  that  the  stationary  grate  bars  are  pro- 
vided with  ribs  on  both  sides  for  the  upper  half,  ap- 
proximately, of  their  length.  This  is  for  the  purpose 
of  preventing  the  droppage  of  fine  coal  through  the 
grate  before  the  coking  process  is  complete,  and  also 


FURNACE    EFFICIENCY 


107 


to  exclude  excess  air  at  this  particular  point  in  the 
combustion  process. 

The  method  of  feeding  the  coal  onto  these  inclined 
grates  is  interesting,  and  may  be  seen  clearly  from 
Fig.  42.  On  either  side  of  the  furnace,  and  extending 
its  entire  length  from  front  to  back,  is  a  coal  magazine 
into  which  coal  may  be  discharged  by  a  down  spout 


FIG.    41. 


from  an  overhead  bunker,  or  shoveled  by  hand.  Just 
at  the  bottom  cf  this  magazine  is  the  coking  plate  (see 
Fig.  42)  upon  which  the  coal  is  first  discharged  from 
the  magazine.  This  plate  furnishes  the  bearing  for  the 


108 


FURNACE   EFFICIENCY 


upper  end  of  the  grate  bars,  the  movable  bars  turning 
on  pins  as  shown  in  the  figure.  Below  the  coking  plate 
is  an  air  duct  through  which  air  is  drawn  from  the 
front  of  the  furnace  and  discharged  at  the  back  into  the 


FIG.    42. 


air  chamber  in  the  arch.  This  keeps  the  coking  plate 
from  becoming  overheated,  thus  adding  greatly  to  its 
length  of  life. 

The  stoker  boxes  are  for  the  purpose  of  pushing  the 
coal  from  the  magazine  out  onto  the  coking  plate. 
They  are  shown  in  Fig.  42  and  also  more  in  detail  in 
Fig.  44.  These  boxes  are  moved  back  and  forth  by 
means  of  segment  gears  and  racks,  the  gears  being 
mounted  on  the  stoker  shaft  which  is  driven  from  an. 
outside  source  of  power.  The  reciprocating  motion  of 
the  stoker  boxes  produces  the  feed  of  the  fuel,  and  can 


FURNACE   EFFICIENCY 


109 


be  regulated  to  suit  the  character  of  the  coal  and  the 
rate  of  combustion. 


FIG.    43. 


The  lower  ends  of  the  grate  bars  are  supported  on 
two  heavy  plates  known  as  the  "grate  bearers/'  one 
for  each  side  of  the  funace.  These  grate  bearers  are 
supported  on  I-beam  cross' girders,  as  shown  plainly  in 
Fig.  41.  In  addition  to  carrying  the  lower  ends  of  the 
grate  bars,  they  furnish  a  support  for  the  rotating 
clinker  grinder.  The  latter  may  be  single  as  shown  in 
Fig.  45,  or  double,  as  shown  in  Fig.  46. 

This  clinker  grinder  consists  of  a  square  steel  shaft 
upon  which  are  placed  small  toothed  cast-iron  seg- 
ments. The  latter  may  be  easily  and  cheaply  renewed 
in  case  of  wear  or  breakage.  As  its  name  implies,  the 
function  of  the  clinker  grinder  is  to  break  up  the  large 
lumps  of  ash  and  clinker  which  might  otherwise  clog 


110 


FURNACE    EFFICIENCY 


the  furnace,  and  discharge  them  into  the  ash  pit  below. 
Just  below  the  clinker  grinder  is  a  small  perforated 
pipe  connected  with  the  exhaust  from  the  stoker  en- 


FIG.    44. 

gine.  This  pipe  is  shown  plainly  in  the  longitudinal 
section  of  the  furnace.  Fig.  47.  The  exhaust  steam 
emitted  directly  beneath  the  clinker  grinder  serves  to 
soften  the  clinker  and  so  assist  in  the  cleaning  process. 
The  rate  of  feed  of  tne  grinder  is  adjustable,  so  that  it 
can  be  varied  to  suit  the  aniout  of  ash  in  the  coal. 

An  important  feature  of  this  furnace  is  the  double 
sprung  arch,  The  arch  is  supported  at  each  side  of  the 
furnace  on  the  arch  plate  shown  in  detail  in  Fig.  48.  It 
will  be  noted  that  on  this  arch  plate  are  cast  a  number 
of  ribs  which  form  a  series  of  air  ducts  immediately 
under  the  arch  and  over  the  coking  plate.  The  manner 
in  which  the  arch  is  sprung  from  the  arch  plate,  and 
also  the  air  ducts  just  below  the  arch,  are  shown  plain- 
ly in  Fig.  41.  Further  details  are  shown  in  Fig.  49. 


FURNACE    EFFICIENCY 


111 


The  lower  arch  is  built  of  special  fire  brick,  varying 
in  thickness  from  6  inches  to  12  inches  according  to  the 
size  of  the  furnace.  Above  this  fire-brick  arch  is  an  air 
space  from  3^  inches  to  5  inches  in  thickness.  It  was 
stated  above  that  air  from  the  duct  under  the  coking 


FIG.    45 


plate  is  discharged  into  this  space  in  the  arch.     Here 
it  is  heated  by  the  radiant  heat  from  the  furnace,  and 


finally  discharged  through  the  ribbed  arch  plate,  over 
the  coal  on  the  coking  plate.    This  supply  of  hot  air 


il£  FURNACE  EFFICIENCY 

being  discharged  over  the  coal  during  the  coking 
process  greatly  assists  in  the  'combustion  of  the  vola- 
tile gases.  It  is  'because  of  this  feature  that  the  Mur- 
phy furnace  can  be  operated  practically  without  smoke. 


FIG.    47. 


The  upper  arch  is  really  a  double  arch  of  common 
brick,  and  over  this  is  placed  a  steel  covering,  rolled  to 
conform  wit'h  the  curve  of  the  arch.  In  such  a  con- 
struction as  this  the  furnace  requires  no  side  walls  but 
is  enclosed  instead  in  sheet  steel  sides  which  the 
makers  supply  with  the  furnace. 

In  the  operation  of  this  furnace  there  are  five  shafts 
or  bars  which  must  be  given  an  oscillating  motion,  as 


FURKACE  EFFICIENCY 


11.1 


follows.  Two  rocker  bars,  two  stoker  shafts,  and  one 
clinker  grinder.  In  the  case  of  a  double  clinker  grinder 
this  becomes  six  instead  of  five.  The  power  to  operate 
these  shafts  is  supplied  by  a  reciprocating  bar  across 
the  front  of  the  furnace.  This  is  a  heavy  forged  steel 
bar  to  which  the  operating  parts  are  connected  by 


FIG.    48. 


means  of  links.  The  construction  and  arrangement  of 
parts  is  shown  in  Fig.  50,  which  shows  the  Murphy 
furnace  applied  to  a  horizontal  tubular  boiler.  The 
operating  links  can  be  adjusted-  or  removed  at  any 
time,  so  that  one  furnace  of  a  battery  may  be  thrown 
out  of  service  without  interfering  with  the  others. 

The  reciprocating  bar  which  operates  the  furnace 
may  be  driven  directly  from  a  small  stoker  engine  as 
shown  in  Fig.  51,  or  if  convenient  an  electric  motor 
may  be  substituted  for  the  engine. 

In  the  operation  of  this  furnace,  as  the  coal  leaves 
the  magazine  it  is  fed  alternately  and  intermittently 
onto  the  coking  plate  by  the  action  of  the  stoker  boxes. 


114  FURNACE   EFFICIENCY 

It  rests  for  a  short  time  on  the  coking  plate,  where  the 
volatile  gases  are  distilled.  These  gases  are  then 
mixed  with  hot  air  which  is  being  discharged  from 
the  ducts  in  the  arch  plate.  This  forms  a  readily  com- 
bustible mixture,  all  the  requirements  for  complete 
combustion  being  present.  Thus  the  volatile  part  of 
the  coal  is  consumed  without  the  formation  of  smoke. 

The  fuel  next  passes  out  onto  the  inclined  grates 
where  it  receives  the  necessary  amount  of  air  coming 
through  the  grates  from  below.  When  the  carbon  is 
practically  all  consumed  and  the  lower  end  of  the  grate 
bars  has  been  reached  the  motion  of  the  moveable  bars 
tends  to  prevent  the  formation  of  large  clinkers.  In  as 
much  as  these  bars  are  pivoted  at  their  upper  ends  they 
have  their  greatest  motion  at  the  lower  ends,  where  the 
motion  is  needed  to  assist  in  the  prevention  of  large 
clinkers.  When  the  bottom  of  the  grate  has  been 
reached  the  ash  and  clinker  are  received  by  the  clinker 
grinder  and  reduced  to  small  size,  after  which  they  are 
dropped  through  to  the  ash  pit  below. 

This  furnace  is  usually  installed  by  the  makers  to 
give  its  best  efficiency  at  from  100  to  150  per  cent  of 
boiler  rating.  This,  however,  by  no  means  represents 
the  limit  of  capacity  of  the  furnace.  As  much  as  200 
per  cent  of  boiler  rating  may  be  secured  with  but  little 
loss  in  efficiency.  The  question  of  high  efficiency  at 
high  rates  of  working  is  very  largely  one  of  the  proper 
proportioning  of  furnace  and  draft.  In  fact  with  a 
good  grade  of  coal  and  sufficient  draft  there  seems  to> 
be  no  reason  why  this  furnace  can  not  be  operated  at  a 
capacity  close  to  the  maximum  ability  of  the  boiler  to 
absorb  heat. 

Questions  and  Aswers. 

Q.     To  what  class  of  automatic  stokers  does  the 
Murphy  Furnace  belong? 
A.     To  the  side  feed  class. 


FURNACE   EFFICIENCY 


115 


FIG.    49. 


116 


FURNACE    EFFICIENCY 


FURNACE    EFFICIENCY 


117 


Q.  Of  what  does  the  chief  part  of  this  furnace  con- 
sist? 

A.  It  consists  of  two  grate  surfaces,  inclined  from 
the  side  and  meeting  in  the  middle  of  the  furnace. 


FIG.    51. 


Q.     How   many  kinds  of   grate  bars  are   used? 
A.     Two  kinds,  stationary  and  movable. 


118  FURNACE    EFFICIENCY 

Q.  How  are  the  movable  bars  placed  in  the  fur- 
nace? 

A.  They  are  pivoted  at  their  upper  ends  and  given 
a  rocking-  motion  at  their  lower  ends  by  means  of  two 
rocker  bars. 

Q.     Where  is  the  coal  supply  fed  to  the  furnace? 

A.     Into  two  magazines,  one. on.  each  side. 

Q.     What  is  the  coking  plate? 

A.  A  flat  plate  at  the  bottom  of  the  coal  magazine 
upon  which  the  coal  is  discharged. 

Q.     How  is  the  coal  fed  to  the  coking  plate? 

A.  By  means  of  the  stoker  boxes,  operated  by  seg- 
ment gears  and  racks. 

Q.     What  is  the  clinker  grinder? 

A.  It  is  a  heavy  steel  shaft  on  which  toothed  cast- 
iron  segments  are  placed,  to  break  up  the  clinker. 

Q.     Where  is  the  clinker  grinder  placed? 

A.  At  the  bottom  of  the  inclined  grates  at  the  cen- 
ter of  the  furnace. 

Q.     What  kind  of  an  arch  is  used  in  this  furnace? 

A.  A  double  arch,  sprung  between  the  sides  cf  the 
furnace. 

Q.     What  is  the  object  of  the  airspace  in  the  arch? 

A.  To  heat  air  to  assist  in  the  combustion  of  the 
fuel.  It  also  makes  a  better  arch. 

Q.     How  is  the  furnace  operated? 

A.  By  a  reciprocating  bar  across  the  front,  driven 
by  a  small  stoker  engine. 


FURNACE    EFFICIENCY 


119 


CHAPTER  XL 
The  Jones  Under-feed  Stoker. 

In  our  discussion  of  mechanical  stokers  nothing 
has  been  said  thus  far  of  the  under-feed  principle.  It 
consists  essentially  in  feeding  the  coal  in  at  the  bot- 
tom of  a  retort  in  which  it  rises  gradually  to  the  com- 
bustion zone  at  the  top.  As  the  coal  rises  to  the  top, 
of  the  retort  its  temperature  rises  gradually,  the  vola- 


FIG.    52. 

tile  gases  being  distilled  in  the  process.  These  gases 
must  then  rise  through  the  fire  at  the  top  when  com- 
plete combustion  takes  place.  Finally  the  coal  itself, 
which  by  this  time  has  been  reduced  to  coke,  reaches 
the  surface  and  is  burned. 

Perhaps  the  best  known  example  of  this  principle 
is  the  Jones  Under-feed  Mechanical  Stoker.   In  Fig.  52 


120 


FURNACE   EFFICIENCY 


is  shown  a  view  of  the  fuel  retort,  which  is  the  only 
part  of  this  stoker  which  is  inside  the  furnace  and 
therefore  in  contact  with  the  fire.  This  retort  can  be 
made  heavy  and  durable,  and  since  there  are  abso- 
lutely no  moving  parts  to  come  into  contact  with  the 
fire,  the  maintenance  charges  on  a  stoker  of  this  kind 
are  extremely  small. 


FIG.    53. 

It  will  be  seen  from  Fig.  52  that  there  is  a  small 
rod  in  the  bottom  of  the  retort,  upon  which  are 
mounted  two  rectangular  shaped  lugs.  This  rod  is 
known  as  the  auxiliary  pusher  rod,  and  is  given  a  re- 
ciprocating motion  from  the  main  ram,  which  will  be 
described  later.  This  auxiliary  pusher  is  for  the  pur- 
pose of  securing  a  more  even  distribution  of  the  fuel 
within  the  furnace,  after  it  has  been  delivered  to  the 
retort  by  the  main  ram. 

The  Jones  Under-feed  Stoker  is  used  entirely  with 
forced  'draft,  and  so  in  this  particular  also  it  differs 
greatly  from  any  stoker  discussed  thus  far.     The  air 
for  combustion    is    supplied    through    tuyere    blocks 
which  are  placed  at  the  top  of  the  retort  an;l  on  both 


FURNACE    EFFICIENCY 


121 


sides.  Hence  the  air  passing  through  these  tuyere 
blocks  blows  from  both  sides  toward  the  center  of  the 
fire,  and  can  at  all  times  be  adjusted  exactly  as  the  rate 
of  combustion  may  require.  The  manner  in  which 


FIG.    54. 


these  tuyere  blocks  are  attached  to  the  retort  is  shown 
clearly  in  Fig.  53.  It  will  be  noted  that  each  tuyere 
block  is  provided  on  its  under  side  with  a  hook  or  eye- 
hole, similar  to  an  eye-bolt.  \Yhen  "all  the  blocks  are 
in  place  a  rod  is  run  through  all  the  eye-holes,  and  the 
tuyere  blocks  are  thus  held-  securely  in  place.  Re- 
placing one  of  these  blocks  which  may  have  become 
worn  or  broken  is  a  simple  operation  and  fairly  inex- 
pensive. A  good  view  of  the  tuyere  blocks  in  position 
in  the  complete  stoker  may  be  seen  from  Fig.  54. 

That  portion  of  the  stoker  which  is  outside  of  the 
furnace  is  shown  in  Fig.  55.  It  consists  of  the  cylinder, 
the  ram  case,  and  the  coal  hopper.  The  ram  case  is 
bolted  securely  to  the  retort,  the  two  being  joined 
together  at  the  boiler  front.  This  case  contains  the 
main  ram,  the  purpose  of  which  is  to  take  the  coal  as  it 
flows  down  from  the  hopper  and  push  it  forward  into 
the  retort  in  the  furnace.  This  ram  is  driven  by  a 
steam  piston  contained  in  the  cylinder  shown  at  the 


122  FURNACE    EFFICIENCY 

right-hand  side  of  the  illustration  in  Fig-.  54.  This  pis- 
ton is  usually  about  12  inches  in' diameter  and  has  a 
stroke  of  approximately  14  inches.  It  has  a  recip- 


FIG.    55. 


rocating  motion  similar  to  the  steam  piston  of  a  direct- 
acting  pump,  this  motion  being  controlled  by  specially 
designed  automatic  valves. 

Fig.  56  shows  a  section  through  the  Jones  stoker, 
from  which  a  good  idea  of  its  construction  may  be 
obtained.  The  steam  piston  and  main  ram  are  clearly 
shown,  as  well  as  the/ auxiliary  pusher  rod  in  the  bot- 
tom' of  the  retort. 

Fig.  57  shows  the  Jones  stoker  applied  to  a  horizon- 
tal return  tubular  boiler.  The  air  duct  supplying  air 
to  the  chamber  below  the  fire  is  shown  plainly  in  this 
view.  Also  it  will  be  noted  that  on  either  side  of  the 
furnace,  and  extending  from  the  retort  to  the  side  wall, 
there  is  a  dead-plate.  The  fire  spills  over  from  the 
retort  onto  these  dead-plates,  and  they  also  serve  to 
catch  and  hold  the  ashes  until  they  are  removed. 


FURXACE    EFFICIENCY 


1-23 


The  automatic  features  of  the  Jones  stoker  are  par- 
ticularly interesting,  and  merit  special  attention.  It 
was  stated  in  an  early  chapter  that  the  rate  of  supply 
of  both  fuel  and  air  must  be  carefully  proportioned  at 
all  times  to  the  demand  for  steam,  that  is,  to  the  raU 


FIG.    56. 


of  combustion,  if  high  furnace  efficiency  is  to  be  main- 
tained. This  is  just  what  the  Jones  stoker  does,  and 
for  this  reason  it  is  able  to  show  good  economy  at 
widely  varying  rates  of  working  and  particularly  at 
light  loads,  a  feature  not  possessed  by  any  of  the 
stokers  discussed  thus  far. 

The  fan  which  supplies  air  to  the  furnace  is  driven 
by  a  special  vertical  engine  which  is  equipped  with  a 
regulating  valve.  \Yhenever  the  steam  pressure  rises 
above  a  certain  amount  the  regulating  valve  throttles 
the  steam  supply  and  thus  slows  down  the 'engine.  If 
the  steam  pressure  falls  too  low  the  regulating  valve 
opens  up  and  admits  more  steam  to  the  engine,  thus 
increasing  its  speed.  In  this  wav  the  amount  of  air 
supplied  to  the  furnace  is  proportioned  to  the  demand 
for  steam. 

The  rate  at  which  the  fuel  is  fed  to  the  furnace  is 
also  made  proportional  to  the  demand  for  steam  by  the 
following  method.  It  will  be  remembered  that  the  ram 
which  forces  the  coal  into  the  hopper  is  actuated  by  a 
steam-driven  piston  working  in  a  cylinder  similar  to 


m  FURNACE    EFFICIENCY 

that  of  a  direct-acting  steam  pump.  Now  the  admis- 
sion of  steam  to  this  cylinder  is  controlled  by  a  rotary 
disc  valve,  a  separate  admission  valve  being  required 
for  each  stoker  cylinder.  Fig.  58  shows  a  bank  of  four 
of  these  disk  valves,  piped  up  ready  for  connection  to 


FIG.    57. 

steam  and  exhaust  lines.  The  frame  carrying  these 
valves  is  placed  near  the  blower  which  supplies  the  air 
to  the  furnace.  The  valves  are  rotated  by  means  of  a 
belt  running  on  a  pulley  on  the  blower  shaft,  the  rela- 
tive sizes  of  blower  pulley  and  valve  pulley  being  so 
adjusted  as  to  maintain  the  proper  relation  between  air 


FURXACE  EFFICIENCY  125 

supply  and  fuel  supply.  The  disk  valves  control  the 
amount  of  steam  admitted  to- the  stoker  cylinder,  and 
thus  the  rate  of  motion  of  the  main  ram  is  controlled. 
If  the  steam  pressure  falls,  the  regulating  valve  causes 
the  blower  engine  to  speed  up.  This  increases  the 


FIG.    58. 

speed  of  the  blower  and  more  air  is  delivered  to  the 
furnace.  At  the  same  time  the  rotary  disk  valves  are 
driven  faster,  more  steam  is  admitted  to  the  stoker 
cylinder,  the  ram  moves  faster,  and  more  coal  is  sup- 
plied to  the  furnace. 

When  the  steam  pressure  rises  above  the  desired 
point  just  the  reverse  takes  place,  and  the  rate  of 


i>6  FURNACE  EFFICIENCY 

bustion  is  reduced.  In  this  way  both  fuel  supply  and 
air  supply  are  controlled  automatically,  and  thus  effi- 
cient conditions  are  maintained  at  all  times. 

The  stoker  cylinder  receives  steam  throughout  the 
whole  stroke  of  the  piston,  no  earlier  cut-off  being  pro- 
vided for  by  the  rotary  valves.  A  moment's  consider- 
ation will  make  it  evident  that  it  would  not  be  prac- 
ticable to  use  the  steam  expansively  in  service  of  this 
kind.  When  the  ram  begins  its  forward  stroke  the 
first  few  inches  of  its  travel  simply  serve  to  pack  the 
coal  firmly  together  in  the  throat  of  the  ram  case. 
Then  as  the  motion  continues  the  whole  charge  is 
pushed  forward  into  the  retort,  the  fuel  already  there 
being  displaced  upward.  It  follows  therefore  that  the 
heaviest  load  on  the  ram  is  near  the  end  of  the  stroke, 
and  hence  the  piston  must  receive  full  steam  pressure 
for  the  whole  stroke,  inasmuch  as  there  is  no  fly-wheel 
to  carry  it  past  this  point  of  greatest  load. 

Fig.  59  gives  a  good  view  of  an  installation  of 
Jones  stokers,  showing  boilers,  stokers,  blower  engine, 
blower,  and  rotary  disk  valves.  The  space  in  front  ot 
the  boilers  occupied  by  the  stoker  cylinder,  ram  case, 
and  hopper,  is  not  large,  being  about  4  feet  8^  inches 
in  length  outward  from  the  boiler  front,  and  17  inches 
in  greatest  width. 

The  operation  of  the  Jones  Under-feed  Stoker  is 
extremely  simple,  and  at  the  same  time  shows  a  high 
degree  of  efficiency.  The  coal  is  fed  into  the  hopper 
either  by  hand  or  from  a  downspout  from  an  over- 
head bunker.  Any  fair  grade  of  coal  burns  well  in 
this  stoker,  provided  it  is  small  enough  not  to  choke 
the  throat  of  the  ram  case,  which  is  about  8  inches  in 
diameter.  The  ram  receives  the  coal  from  the  hopper 
and  pushes  it  forward  into  the  retort.  The  auxiliary 
pusher  rod  in  the  bottom  of  the  retort  agitates  the 
fuel  therein,  and  causes  it  to  work  upward  toward 
the  surface.  As  the  coal  nears  the  surface  the  volatile 


FURNACE   EFFICIENCY  12? 

gas  is  gradually  driven  oft  by  the  heat  of  the  fire,  and 
burned  as  it  passes  through  the  fire.  Finally  the  coal 
reaches  the  surface  where  combustion  is  completed. 


In  the  usual  form  of  Jones  stoker,  the  ashes  are 
allowed  to  collect  on  the  dead-plates  on  either  side  of 
the  retort.  They  are  then  removed  by  hand,  being 
pulled  out  at  two  doors  in  the  front  of  the  setting. 


FURNACE    EFFICIENCY 


Fig.  GO  shows  the  appearance  of  a  boiler  front  equipped 
with  Jones  stokers.  The  two  upper  doors  shown  1.1 
the  figure  are  for  the  purpose  of  removing  the  ash  arr.l 
clinker.  A  recent  improvement  to  this  stoker  provides 
a  mechanical  arrangement  for  agitating  and  cleanin  ? 
the  fires  and  removing  the  ashes.  In  this  form  th2 


FIG.    60. 

stoker  is  entirely  automatic,  the  only  attention  which 
it  requires  being  directed  to  the  removal  of  the  ashes 
from  the  ash-pit. 

In  summing  up  the  points  of  superiority  charac- 
teristic of  this  stoker,  it  should  be  noted  first  of  all 
that  it  possesses  all  the  advantages  of  mechanical 
forced  draft.  This  consists  chiefly  in  a  nice  adjust- 
ment between  air  supply  and  rate  of  combustion.  This 
adjustment  is  made  automatically  and  practically  in- 
stantaneously, so  that  no  matter  what  the  load  fluctua- 


FURNACE    EFFICIENCY  129 

tions  may  be,  the  proper  draft  is  always  maintained.' 
The  automatic  control  of  the  fuel  supply  insures  eco- 
nomical adjustment  at  all  times  and  leaves  almost 
nothing  to  be  desired  in  the  way  of  automatic  furnace 
control.  In  this  particular  the  Jones  stoker  is  the 
equal,  if  not  the  superior,  of  any  other  furnace  which 
has  come  to  our  attention. 

The  combustion  is  such  that  no  fire-brick  arches 
are  required  to  render  the  furnace  practically  smoke- 
less. The  coal  rises  in  the  retort  like  a  slow-moving 
fountain,  the  gases  being  distilled  as  the  coal  reaches 
the  surface.  As  they  pass  through  the  fire,  they  are 
thoroughly  mixed  with  the  proper  amount  of  air  at  a 
high  temperature,  which  as  we  have  seen  in  an  early 
chapter,  is  all  that  is  required  for  smokeless  combus- 
tion. The  absence  of  all  arches  makes  an  economical 
furnace  to  build  and  maintain.  There  is  probably 
little  doubt  that  the  Jones  stoker  in  the  form  described 
here,  will  have  as  low  maintenance  charges  as  any 
mechanical  stoker  on  the  market. 

Questions  and  Answers. 

Q.  What  principle  is  used  in  the  Jones  stoker? 

A.  The  under-feed  principle. 

Q.  What  are  the  chief  parts  of  the  Jones  stoker? 

A.  The  retort,  ram  case,  ram  and  stoker  cylinder. 

Q.  Which  of  the  above  parts  are  inside  the  fur- 
nace? 

A.  The  retort. 

Q.  How  is  the  coal  fed  into  this  retort? 

A.  By  a  ram  actuated  by  a  steam-driven  piston. 

Q.  How  is  the  air  supply  provided  for  this  stoker? 

A.  By  a  blower  driven  by  a  special  engine. 

Q.  How  is  the  speed  of  this  engine  controlled? 

A.  By  a  regulating  valve,  wrhich  in  turn  is  con- 
trolled by  the  steam  pressure. 


130  FURNACE   EFFICIENCY 

Q.  How  is  the  speed  of  the  piston  which  drives 
the  main  ram  controlled? 

A.  By  rotating  disk  valves  driven  from  a  pulley  on 
the  blower  shaft. 

Q.  Are  both  air  supply  and  coal  supply  controlled 
automatically? 

A.     Yes. 


FURNACE    EFFICIENCY  131 


CHAPTER  XII. 
The  Ignition  Arch. 

In  the  course  of  the  preceding  pages  frequent 
reference  has  been  made  to  the  firebrick  arch  in  a 
boiler  furnace.  It  has  been  shown  that  such  an  arch 
assists  to  a  considerable  extent  in  securing  smokeless 
and  efficient  combustion  by  providing-  a  roof  of  re- 
fractory material  for  the  furnace,  and  so  preventing 
the  volatile  gases  from  the  coal  from  coming  into  con- 
tact with  the  boiler  heating  surfaces  until  combustion 
has  been  completed.  In  the  present  chapter  the  fire- 
brick arch  will  be  considered  somewhat  more  in  detail, 
with  a  view  to  making  clear  the  principles  underlying1 
its  action. 

For  our  present  purpose  it  will  be  well  to  divide  all 
boiler  furnace  arches  into  two  general  classes.  First, 
the  ignition  arch,  the  chief  function  of  which  is  to 
assist  in  the  ignition  of  the  fresh  coal  as  it  comes  into 
the  furnace.  Second,  the  deflecting  arch,  the  function 
of  which  is  to  deflect  the  burning  gases  away  from  the 
boiler  heating  surfaces,  and  at  the  same  time  to  assist 
in  the  proper  mixing  of  gases  and  air  so  as  to  promote 
complete  combustion.  It  will  be  evident  that  both 
kinds  of  arches  have  an  important  part  to  play  in  the 
solution  of  the  problem  of  efficient  combustion. 

The  ignition  arch  has  undergone  quite  radical 
changes  in  design  within  the  last  few  years,  the 
changes  being  prompted  by  a  better  understanding 
of  the  principles  underlying  its  action.  In  the  early 
designs  the  ignition  arch  was  often  made  as  short  as 
two  feet;  a  length  of  three  feet  was  considered  quite 


132 


FURNACE    EFFICIENCY 


generous,  while  an  ignition  arch  four  feet  in  length 
was  regarded  as  extreme.  These  arches  were  built  flat, 
with  a  slight  upward  pitch  toward  the  rear,  and  were 
set  quite  close  to  the  grate.  These  early  designs  lo- 
cated the  arch  entirely  with  reference  to  its  distance 
from  the  grate,  without  regard  to  the  thickness  of  fuel 
bed  that  would  have  to  be  carried.  The  result  was 


FIG.    61. 

that  those  arches  were  frequently  only  two  or  three 
inches  above  the  fuel  when  a  thick  fire  was  carried. 
Present  practice  places  an  ignition  arch  with  reference 
to  its  distance  from  the  surface  of  the  fuel  bed,  in 
which  case  the  character  of  fuel  and  average  thickness 
of  fire  must  be  carefully  considered  when  designing 
the  arch. 

The  action  of  the  short  flat  ignition  arch  just  de- 
scribed was  probably  about  as  .follows :  The  volatile 
gases  liberated  from  the  coal  ignited  at  the  surface  of 
the  fuel  bed.  The  heat  liberated  by  this  combustion 
heated  the  arch  immediately  above  to  a  state  of  in- 
candescence, and  the  hot  arch  in  turn  reflected  the  heat 
back  again  onto  the  incoming  fuel.  In  this  way  a 
prompt  ignition  of  the  fresh  coal  was  effected,  the  arch 
acting  as  a  mirror  to  reflect  the  heat  forward  to  the 
point  where  it  was  most  needed. 


FURNACE   EFFICIENCY 


133 


Experience  with  ignition  arches  has  taught  en- 
gineers that  the  greatest  intensity  of  radiation  is  in  a 
direction  perpendicular  to  the  radiating  surface,  and 
from  its  center.  Also,  the  temperature  produced  at 
any  point  in  the  green  fuel  bed  by  the  action  of  the 


FIG. 


radiant  energy  from  the-  arch  is  inversely  proportional 
to  the  distance  from  Jthe  arch.   That  is,  the  farther  a 


FIG.    63. 

given  point  is  from  the  arch  the  less  heat  it  will  re- 
ceive. 

If  a  flat  arch  be  placed  parallel  to  the  grate  it  fol- 
lows from  the  principles  just  stated  that  the  maximum 
radiation  and  hence  the  maximum  igniting  effect  will 


134  FURNACE    EFFICIENCY 

be  directly  under  the  center  of  the  arch.  Fig.  61  shows 
the  distribution  of  radiant  heat  under  such  an  arch, 
the  semicircle  showing  the  character  of  the  distribu- 
tion, and  the  shading  the  intensity  of  radiation.  Fig. 
62  shows  how  the  point  of  most  intense  radiation  is 
thrown  forward  when  the  arch  is  tilted  upward 
toward  the  rear,  and  Fig.  63  shows  how  the  radiation 
is  reduced  and  thrown  still  farther  forward  in  the  fur- 
nace when  the  arch  is  inclined  still  more. 

An  arch  of  this  kind  will  give  an  igniting  effect 
across  practically  the  whok  of  the  furnace,  and  al- 
though the  figures  show  that  this  effect  is  greatest  at 
the  center,  still  the  radiation  from  the  side  walls  assists 
ignition  at  the  sides,  so  that  a  flat  arch  gives  practic- 
ally uniform  ignition  across  the  entire  width  of  the 
furnace.  The  figures  show  further  that  in  order  to 
get  the  maximum  igniting  effect  near  the  front  of  the 
furnace  where  it  is  most  needed  the  arch  should  be 
horizontal,  or  at  least  should  have  but  a  slight  upward 
incline  toward  the  rear. 

When  a  sprung  ignition  arch  is  used  the  igniting 
effect  is  not  so  satisfactory  in  general  as  it  is  with  the 
flat  arch.  The  center  of  the  arch  being  farther  from 
the  fuel  bed  than  is  the  case  with  the  sides  of  the  arch, 
the  igniting  effect  is  greater  at  the  sides  of  the  furnace 
than  at  the  center.  The  radiation  from  the  side  walls 
also  tends  to  increase  this  discrepancy,  so  that  even 
although  the  curvature  of  the  arch  may  be  slight  the 
igniting  effect  is  not  uniform  across  the  furnace.  In 
view  of  this  fact  there  seems  to  be  no  reason  why  the 
flat  arch  should  not  displace  the  sprung  variety  where- 
ever  the  conditions  make  it  possible,  particularly  when 
the  mechanical  difficulties  in  the  way  of  the  construc- 
tion and  maintenance  of  a  sprung  arch  are  considered. 

From  the  foregoing  discussion  it  should  be  evident 
that  the  short  ignition  arch,  whether  flat  or  sprung, 
merely  takes  heat  from  the  burning  volatiles  and  de- 


FURNACE   EFFICIENCY  135 

fleets  that  heat  forward  onto  the  green  incoming  fuel. 
In  general  the  flat  arch  is  to  be  preferred  to  the  curved 
one  because  the  ignition  is  more  uniform  across  the 
furnace  with  the  former.  Later  experience  with  the 
ignition  arch  has  demonstrated  the  possibility  of  using 
the  heat  from  the  rear  of  the  fuel  bed  for  purposes  of 
ignition.  At  this  point  in  the  furnace  the  fixed  carbon 
of  the  coal  is  being  consumed  and  it  is  here  that  the 
greatest  amount  of  heat  is  liberated,  and  hence  the 
highest  temperatures  exist. 

In  order  to  utilize  this  heat  from  the  rear  of  the 
furnace  a  radical  change  was  made  in  ignition  arch 
design.  This  change  consisted  chiefly  in  making  the 
arch  very  much  longer  than  before,  lengths  of  six  to 
eight  feet  being  not  at  all  uncommon.  The  action  of 
such  a  long  arch  is  almost  exactly  like  that  of  a  mirror, 
reflecting  heat  from  the  rear  of  the  furnace  to  the  front. 
Keeping  in  mind  the  well  known  law  of  reflecting  sur- 
faces that  the  angle  of  incidence  is  equal  to  the  angle 
of  reflection,  it  is  possible  to  calculate  the  length  and 
position  of  an  arch  for  any  particular  furnace,  provided 
the  characteristics  of  the  fuel  and  the  load  conditions 
are  known  accurately. 


FIG.    64. 


Fig.  64  shows  how  heat  coming  from  a  point  "a" 
in  the  rear  of  the  furnace  is  reflected  by  the  arch  to 
various  points  in  the  front  of  the  furnace.  The  arch 


136  FURNACE    EFFICIENCY 

shown  is  flat  and  inclined  upward  toward  the  rear  of 
the  furnace.  This  pitch  is  usually  not  more  than  three 
inches  to  the  foot  and  in  many  cases  it  is  less.  In  fact, 
with  certain  kinds  of  coal  a  horizontal  arch  six  or 
seven  feet  long  may  be  used  to  good  advantage.  Fig. 
65  shows  how  the  heat  is  reflected  by  a  horizontal  arch 
from  the  rear  to  the  front  of  the  furnace. 

Let  us  now  consider  a  few  features  of  ignition  arch 
design  as  affected  particularly  by  the  kind  of  fuel 
which  is  to  be  used.  Consider  first  of  all  a  clean  free- 
burning  bituminous  coal,  fairly  low  in  ash  and  con- 
taining thirty  per  cent  of  volatiles.  Such  a  coal  will 
ignite  with  comparative  ease,  and  will  burn  out  free 
from  clinker  or  other  troublesome  ash.  If  such  a  coal 


W/////W///P///////^^^ 


FIG.    65. 

is  to  be  burned  on  a  chain  grate  or  similar  stoker,  the 
arch  should  be  designed  as  follows: 

Inasmuch  as  the  fuel  ignites  easily,  the  igniting 
action  may  properly  be  confined  to  a  comparatively 
narrow  zone  at  the  front  of  the  furnace.  If  the  stoker 
is  approximately  ten  feet  long  the  arch  need  not  be 
more  than  six  feet  in  length.  It  should  be  set  about 
fifteen  inches  above  the  grate  at  the  front,  which  will 
give  a  space  ranging  from  five  to  ten  inches  between 
fuel  and'  arch.  The  arch  should  have  a  pitch  of  about 
2T/2  or  3  inches  to  the  foot,  inclining  upward  toward 
the  rear.  The  reason  for  the  pitch  of  the  arch  is  to 
provide  an  increasing  furnace  cross-section  from  front 
to  rear,  so  as  to  handle  the  increasing  volume  of  fur- 
nace gases  without  undue  restriction. 


FURNACE    EFFICIENCY  137 

Consider  next  a  coal  containing  as  high  as  20  per 
cent  to  30  per  cent  of  ash,  having  a  high  moisture  con- 
tent, and  possibly  in  the  neighborhood  of  20  per  cent 
of  volatiles.  Coals  similar  to  this  are  found  in  many 
of  the  western  States  and  are  now  being  burned  suc- 
cessfully on  chain  grate  stokers.  Such  a  fuel  will 
ignite  much  less  readily  than  the  first  one  considered, 
and  for  this  reason  the  igniting  action  must  be  con- 
tinued over  a  much  wider  zone  than  before.  Also,  the 
front  of  the  furnace  must  be  maintained  at  a-s  high  a 
temperature  as  possible,  to  assist  the  ignition.  For 
this  reason  the  hot  gases  must  not  pass  so  rea'dily  from 
the  furnace,  but  must  be  "bottled  up"  by  restricting 
their  path  somewhat. 

Assuming  the  same  size  of  furnace  as  before,  an 
arch  to  burn  this  fuel  successfully  should  be  about  7^4 
feet  long,  not  more  than  11  or  1*2  inches  above  the 
grate  at  the  front,  and  should  have  only  a  slight  up- 
ward pitch  toward  the  rear.  The  action  of  this  long, 
almost  horizontal  arch  will  be  to  reflect  heat  from  the 
rear  of  the  furnace  over  a  zone  of  considerable  width 
in  the  front.  Thus  the  igniting  effect  of  the  arch  will 
be  continued  for  a  considerable  time  after  the  fuel 
enters  the  furnace,  a  necessary  condition  for  satis- 
factory burning  of  such  coal,  particularly  at  high  rates 
of  combustion  and  high  speed  of  grate  travel. 

The  arch  being  set  almost  parallel  with  the  grate, 
the  heated  gases  do  not  have  such  a  ready  escape  from 
the  furnace  as  when  the  arch  has  considerable  pitch. 
Being  retained  for  a  time  in  the  furnace  in  this  way, 
these  hot  gases  raise  the  temperature  of  the  entering 
coal,  and  thus  assist  ignition. 

Consider  as  a  third  example,  the  case  of  certain  coal 
found  in  some  of  the  southwestern  States,  particularly 
Texas.  This  coal  contains  50  per  cent  or  more  of  ash- 
forming  materials,  and  at  one  time  was  considered 
practically  useless  for  steam-making  purposes.  It  is 


138  FURNACE    EFFICIENCY 

extremely  slow  and  difficult  to  ignite,  and  would  seem 
-to  be  almost  "impossible''  when  used  in  connection 
with  a  mechanical  stoker  of  the  "progressive  combus- 
tion" type. 

To  ignite  such  a  coal  successfully  requires  an  arch 
just  as  long  as  the  size  of  the  furnace  will  permit. 
The  limit  to  the  length  is  imposed,  of  course,  by  the 
fact  that  sufficient  space  must  be  left  between  the  end 
of  the  arch  and  the  bridge  wall  for  the  escape  of  the 
furnace  gases.  The  arch  should  be  horizontal  and  set 
only  about  10  or  11  inches  above  the  grate.  Such  an 
arch  will  give  an  extremely  wide  ignition  zone  in  the 
front  of  the  furnace,  and  will"  bottle  up"  the  hot  gases 
to  such  an  extent  as  to  assist  materially  in  maintaining 
a  high  furnace  temperature,  particularly  near  the  front. 
To  operate  a  furnace  designed  in  such  a  manner  as  this 
will,  of  course,  require  a  good  draft  on  account  of  the 
restriction  at  the  furnace  throat.  But  it  is  the  only 
design  of  furnace  which  makes  it  possible  to  burn  fuel 
of  this  kind  on  a  mechanical  stoker,  and  it  really  repre- 
sents a  long  step  forward  in  furnace  design  to  meet  a 
particular  set  of  conditions. 

From  what  has  been  said  it  should  be  apparent  that 
the  long  ignition  arch,  set  comparatively  low,  and 
either  horizontal  or  with  a  pitch  toward  the  rear  not 
to  exceed  3  inches  to  the  foot,  is  as  correct  in  principle 
as  it  has  proved  successful  in  operation. 

Questions  and  Answers. 

Q.  Into  what  two  general  classes  may  furnace 
arches  be  divided? 

A.     Into  deflection  arches  and  ignition  arches. 

O.     What  is  an  ignition  arch? 

A.  A  firebrick  arch  placed  over  the  front  of  the 
furnace  to  reflect  heat  on  the  incoming  coal. 

Q.     How  long  should  this  arch  be  ? 


FURNACE    EFFICIENCY  139 

A.  Early  design  made  it  only  3  or  4  feet  long,  but 
it  is  now  made  as  much  as  6  to  8  feet  long  in  a  furnace 
10  feet  long. 

Q.  How  should  the  arch  be  placed  with  respect 
to  the  grate? 

A.  About  10  to  15  inches  above  the  grate,  and 
either  parallel  to  it  or  with  a  slight  pitch  toward  the 
rear. 

Q.     How  much  should  this  pitch  be? 

A.     Probably  not  to  exceed  3  inches  to  the  foot. 


140  FURNACE   EFFICIENCY 


CHAPTER  XIII.  . 
Breeching  and  Chimney. 

It  may  sometimes  happen  that  a  well  designed 
furnace,  properly  operated,  will  fail  to  give  satisfac- 
tory capacity  or  efficiency.  In  such  a  case  it  is  often 
necessary  to  look  for  the  trouble  outside  of  the  furnace 
itself. 

One  very  important  part  of  a  boiler  room  instal- 
lation, and  one  which  frequently  receives  much  less 
attention  than  it  deserves,  is  the  breeching  through 
which  the  furnace  gases  pass  from  the  boiler  setting 
to  the  chimney.  Unless  this  breeching  is  intelligently 
designed  and  carefully  constructed  it  may  cut  down 
the  capacity  and  economy  of  the  furnace  to  a  con- 
siderable extent. 

The  cross  section  of  the  breeching  is  perhaps  the 
first  point  to  receive  consideration.  It  should  be 
designed  with  reference  to  the  total  volume  of  fur- 
nace gases  which  it  will  be  required  to  handle,  rather 
than  as  a  function  of  the  grate  area  served.  An  ap- 
proximate rule  for  the  size  of  a  breeching,  and  one 
which  has  frequently  been  used  as  a  guide  at  least,  is 
to  make  the  section  of  the  breeching  about  1/6  that 
of  the  grate  served.  But  this  rule  takes  no  account  of 
the  kind  of  fuel  which  is  to  be  used,  nor  the  rate  of 
combustion,  the  latter  varying  over  a  wide  range  in 
different  plants. 

Evidently  if  the  character  of  the  fuel  which  is  to 
be  used  is  known,  and  if  the  maximum  load  which 
the  boilers  will  be  required  to  carry,  as  well  as  their 
approximate  efficiency  is  known,  the  amount  of  fuel 


FURNACE    EFFICIENCY 


141 


required  per  hour,  and  the  amount  of  air  needed  per 
pound  of  fuel,  can  be  predetermined  with  a  fair  de- 
gree of  accuracy.  Thus  the  weight  of  furnace  gases 
produced  per  minute  or  per  second,  can  be  estimated, 
and  if  the  breeching  temperature  be  taken  as  400°  F. 
to  500°  F.  according  to  conditions,  the  volume  of  gases 
passing  through  the  breeching  per  second  can  be  cal- 
culated. 


FIG.    66. 


It  is  well  to  make  the  breeching  of  such  a  size 
that  the  velocity  of  gas  flow  will  not  exceed  35  feet 
per  second.  If  the  velocity  exceeds  this  amount  the 
friction  of  the  gases  against  the  wall  of  the  breeching 
causes  a  drop  in  draft  pressure  which  for  a  long  run 
of  breeching  may  become  quite  serious. 

This  matter  of  draft  pressure  loss  depends  not 
only  on  the  size  of  the  breeching  but  also  upon  its 
shape,  length,  number  and  character  of  bends,  ma- 
terial of  construction,  etc.  Experience  has  shown 
that  a  circular  section  gives  less  draft  loss  than  a 
square  or  rectangular  section,  other  conditions  being 
the  same.  This  is  probably  due  to  the  fact  that  any 
fluid  meets  with  less  frictional  resistance  when  flow- 


142  FURNACE    EFFICIENCY 

ing  through   a  pipe  of  circular  section   than   in   any 
other  shape. 

The  draft  loss  due  to  length  is  practically  pro- 
portional to  the  length  for  any  shape  of  section. 
Hence  it  follows  that  not  only  from  considerations 
of  economy  in  first  cost,  but  also  to  produce  economy 
of  operation,  a  plant  should  be  laid  out  with  just  as 
short  a  run  of  breeching  as  conditions  will  permit. 
In  a  well  designed  breeching  the  draft  loss  will  prob- 
ably not  exceed  0-1  inch  of  water  per  100  feet  of 
straight  run. 

The  number  of  bends  in  a  breeching  should  be 
kept  as  few  as  possible,  because  at  each  one  there  is 
an  appreciable  loss  in  draft  pressure.  A  single  right- 
angle  bend  will  cause  a  draft  loss  of  about  0.05  inch 
of  water,  due  to  the  eddies  formed  in  the  gas  flow 
when  striking  the  turn.  Figure  66  shows  a  plan 
view  of  a  breeching  in  which  there  is  a  right  angle 
bend.  The  gases  flowing  from  right  to  left  as  shown 
by  the  arrow  strike  the  bend  at  the  point  A  with  a 
certain  amount  of  momentum,  due  to  their  weight  and 
velocity.  The  flow  of  the  gases  is  retarded  and  a 
"swirl"  or  eddy  is  formed,  which  causes  a  loss  in 
draft  pressure.  The  effect  of  the  eddy  is  similar  to  a 
restriction  in  the  breeching,  because  at  the  point 
B  there  is  practically  no  gas  flow.  If  it  be  considered 
in  this  way  it  is  comparatively  easy  to  see  how  a  loss 
in  draft  pressure  occurs.  This  effect  can  be  reduced 
to  a  considerable  extent  by  using  a  long  radius  bend 
as  shown  by  the  dotted  lines.  But  a  bend  of  this 
kind  requires  more  space  which  in  many  city  plants 
is  not  to  be  had.  In  such  a  case  the  draft  loss  due 
to  a  right  angle  bend  must  be  put  up  with,  and  suffi- 
cient height  added  to  the  stack  to  compensate  for  the 
loss. 

Breechings  are    usually    made    of    steel    or    brick- 
work,   and    sometimes    possibly    of   concrete.      From 


FURNACE    EFFICIENCY 


143 


the  point  of  draft  loss  an  all  steel  breeching  is  prob- 
ably to  be  preferred,  but  it  should  be  well  lagged  or 
covered  with  an  insulating  material  to  prevent  radia- 
tion and  infiltration  of  air.  This  is  an  important 
consideration,  because  the  chimney  draft  depends  up- 
on the  temperature  of  the  gases  therein,  and  if  they 
are  cooled  while  passing  through  the  breeching  the 
draft  will  be  reduced. 


A 


FIG.    67. 

In  the  case  of  a  comparatively  long  run  of  breech- 
ing into  which  the  uptakes  from  two  or  more  boilers 
discharge,  the  manner  in  which  the  connection  be- 
tween uptake  and  breeching  is  made  has  an  important 
bearing  on  the  draft  loss.  In  figure  *67  is  shown  an 
elevation  of  a  breeching  into  which  two  uptakes  dis- 
charge at  right  angles.  Unless  the  corners  are  re- 
lieved somewhat  practically  the  same  action  will  take 
place  as  in  a  right-angle  bend.  Figure  66.  The  gas 
from  uptake  A  will  strike  the  opposite  wall  of  the 
breeching  at  C,  and  the  gas  from  B  will  strike  at  D. 
The  result  will  be  the  formation  of  eddies  with  com- 
paratively quiescent  portions  at  E  and  F.  As  was 
described  in  connection  with  Figure  66  this  restricted 
portion  reduces  the  effective  breeching  area  and  a 
loss  in  draft  pressure  takes  place  at  that  point. 


144 


FURNACE    EFFICIENCY 


The  draft  loss  which  takes  place  at  these  points 
can  be  remedied  somewhat  by  relieving  the  corner  on 
the  side  of  the  uptake  towards  which  the  gas  is  to 
flow.  Thus  if  the  corners  be  extended  as  shown  in 
the  dotted  curves,  the  gases  will  be  deflected  some- 
what to  the  left  and  no  quiescent  pocket  will  be 
formed  at  E  or  F. 

Conditions  sometimes  make  it  necessary  to  place 
the  chimney  out  of  the  line  of  the  breeching.  In 


FIG.    68. 

this  case  a  construction  similar  to  that  shown  in 
Figure  68  results.  Here  the  gases  from  the  two 
halves  of  the  breeching  meet  in  collision  at  the  point 
A  and  their  flow  is  thereby  seriously  restricted. 

*  Mr.  T.  A.  Marsh  states  that  a  draft  pressure  loss  of 
as  much  as  0.25  of  an  inch  of  water  has  befen  known  to 
result  from  this  cause.     Again  in  this  case  consider- 
able   improvement    will    result    if    the    corners    be 
rounded  as  shown  by  the  dotted  lines  in  the  figure. 
Marsh  states  that  a  curved  deflecter  D  placed  in  the 

*  Design    of  Breechings   and   Smoke   Flues.      T.   A.   Marsh,    Industrial 
Engineering,   Nov.    1912. 


FURNACE   EFFICIENCY 


145 


breeching  may  prove  beneficial  in  changing  the  direc- 
tion of  flow  of  the  gases  without  excessive  draft 
loss. 

A  condition  similar  to  the  one  just  discussed  ar- 
rises when  breechings  enter  a  chimney  on  opposite 
sides.  Here  again  a  collision  of  the  gases  takes  place 
and  a  drop  in  draft  pressure  results.  Figure  69  shows 
a  construction  which  is  being  used  with  success  in 
such  a  case  as  this.  AB  is  a  baffle  placed  across  the 
chimney  where  the  breeching  enters  which  assists  in 
deflecting  the  .gases  in  the  direction  of  the  draft. 
Even  with  this  construction  there  must  still  be  con- 
siderable draft  loss  at  this  point  because  the  gases 
will  strike  this  baffle  almost  at  right  angles  and  must 
lose  considerable  momentum  thereby. 

Marsh  recommends  a  curved  baffle  as  shown  at 
CD  in  Figure  G9.  The  shape  and  position  of  this 


FIG 


baffle  is  such  that  the  gases  do  not  meet  it  at  right 
angles,  but  are  deflected  upward  in  a  spiral  path 
without  much  loss  of  velocity,  and  writh  only  a  small 
draft  loss. 

When  designing  a  breeching  the  main  point  to 
be  kept  in  mind  is  the  fact  that  the  furnace  gases 
must  flow  through  it  with  as  little  friction  as  possible. 
Anything  which  produces  friction  must  be  avoided  so 
far  as  possible,  particularly  sharp  bends,  and  places 
where  two  streams  of  furnace  gas  may  meet  in  direct 
collision. 


146  FURNACE   EFFICIENCY 

The  one  remaining  feature  of  the  boiler  plant 
which  has  an  important  part  to  play  in  the  combus- 
tion problem  is  the  smoke  stack  or  chimney.  While 
the  complete  discussion  of  the  principles  entering-  into 
the  design  of  a  smoke  stack  does  not  come  within  the 
scope  of  this  work,  still  a  very  few  considerations 
which  .govern  the  design  may  be  mentioned. 

The  sectional  area  of  a  chimney  should  be  suf- 
ficent  to  carry  away  the  furnace  gases  at  a  velocity 
not  to  exceed  25  to  30  feet  per  second.  Since  the  av- 
erage temperature  of  the  chimney  gases  is  consider- 
ably less  than  that  of  the  gas  in  the  breeching  the 
size  of  the  chimney  can  be  somewhat  smaller  than 
the  breeching.  An  average  figure  is  to  make  the 
chimney  15  to  20%  less  than  the  combined  area  of 
breeching  entering  it.  This  provides  for  a  reduced 
gas  velocity  in  the  chimney  and  keeps  down  the  draft 
pressure  loss. 

The  proper  height  for  the  chimney  is  almost  en- 
tirely a  question  of  the  draft  require:!.  Draft  de- 
pends upon  temperature  of  chimney  gases  and  0:1 
elevation  above  the  sea  level  as  well  as  upon  height  of 
chimney,  but  the  height  is  the  chief  consideration. 

The  following  formula  may  be  used  to  calculate 
the  height  of  stack  required  to  give  a  certain  draft. — 
(Stirling  rule.) 

1        1 

D  =  0.52  H  X  P  (-         -) 
T      T, 
in  which  D  =  draft  produced,  in  inches  of  wate1*. 

H  =  height  of  stack  in  feet  above  grate. 

P  —  atmospheric  pressure,  pounds  per  square  inch. 

T  =  absolute  temperature  of  atmosphere,  degrees 
F. 

T!  =  absolute  temperature  of  chimney  gases,  de- 
grees F. 


FURNACE   EFFICIENCY  UT 

From  this  formula  the  height  of  stack  required 
to  give  any  desired  draft  may  be  calculated. 

Questions  and  Answers. 

Q.  What  is  the  connection  between  boiler  uptake 
and  chimney  called? 

A.     The  breeching. 

Q.     How  large  should  this  breeching  be? 

A.  Large  enough  to  carry  away  the  furnace 
gases  with  a  velocity  not  to  exceed  35  feet  per  sec- 
ond. 

Q.  Give  a  "rule  of  thumb''  for  the  size  of  a 
breeching? 

A.  It  should  be  equal  to  1/6  of  the  grate  area 
served. 

Q.  What  is  the  best  shape  for  the  section  of  the 
breeching? 

A.     The  section  should  be  circular. 

Q.     Why? 

A.  Because  the  draft  loss  i".  less  in  a  circular 
breeching  than  in  one  having  any  other  shape  of  sec- 
tion. 

Q.  How  is  a  draft  affected  by  a  right-angle  bend 
in  a  breeching? 

A.  There  is  a  loss  of  about  0.05  of  an  inch  for  each 
bend. 

Q.     Is  there  any  draft  loss  due  to  friction? 

A.  Yes,  about  0.1  of  an  inch  per  100  feet  of  straight 
breeching. 

Q.  How  may  the  dra-ft  loss  due  to  bends  be  re- 
duced? 

A.  Bv  using  long  radius  bends  so  that  the  change 
in  direction  of  gas  flo\v  is  more  gradual. 

Q.  When  two  breechings  enter  a  stack  at  opposite 
sides,  what  should  be  done  to  reduce  the  draft  loss 
at  that  point? 


148  FURNACE   EFFICIENCY 

A.     A  curved  baffle  should  be  placed  in  the  base 
of  the  stack  to  deflect  the  gases  upward. 

Q.     What  should  be  the  section  of  a  smoke  stack? 
A.     About  20%  less  than  the  breeching-  section. 


FURNIACE   EFFICIENCY  UD 


Alphabetical  Index. 


Absorption    of   Heat 67 

Action  of  Blonck   Meter  

Actjon  of  Flat   Ignition   Arch 98 

Action  of  Ignition   Arch   

Action  of  Long   Ignition   Arch 135 

Adjustment  of  Wilsey  Gauge 

Air,  Excess  of,  in  Boiler  Furnace 

Air  Leakage,    Amount    of 

Air  Leakage,    Remedy    for 22 

Air  Leakage  Through  Boiler  Walls 23 

Air  Leaks    How   to   Stop 23 

Air  Leaks,   Location  of 22 

Air  Over   Fire.   Necessity   for 26 

Air  Through  Fire  and  Over  Fire 26 

Appearance  of  Wilsey   Gauge 

Application  of  Progressive  Combustion  to  Hand  Firing..  90 

Area  of  Gas   Path 58 

Asbestos  Cement  Covering  for  Boiler  Brickwork 23 

Automatic  Features  of  Jones  Stoker 123 

B 

Baffle    Piers    48 

Bement,  A.,  Smokeless  Furnace  Design 57 

Binder  Links 95 

Bituminous  Coal,  Air  Required  for 26 

Boiler    Efficiency    Gauge 65 

Boiler  Under  Light  Load ; 26 

Blonck  Boiler    Efficiency   Meter 75 

Blonck  Meter,    Action    of 79 

Blonck  Meter.   Setting  of 79 

Blue  Gauge  in   Blonck  Meter 75 

Breeching,   Curved   Deflector   in 144 

Breeching    Design    140 

Breechi'ngs.  Draft  Pressure  Loss  in 141 

Breechings,  Material  of  142 

Breechings,  Velocity  of  Gas  in 141 


150  FURNACE   EFFICIENCY 

Bulkhead    62 

B.  and  W.  Water  Tube   Boiler 32 

B.  and  W.  Boiler,   Draft   Losses   Through 32 

C 

Carbon  Dioxid,  Amount  in  Flue  Gases 4 

Chain-Grate  Stoker    . 55-90 

Chain-Grate  Stoker,  Construction    91 

Chain-Grate  Stoker,  Feed    Gate    for 97 

Chain-Grate  Stoker,  First   Design 91 

Chain  Grate  Stoker   with    Light   Load 26 

Chain-Grate  Stoker,  Design   of 92 

Chain-Grate  Stokers,  Chain  Tension   in . 95 

Chain-Grate  Stokers,  Double   Web   95 

Chain-Grate  Stokers,  Method  of  Driving 96 

Chain-Tension   in    Chain-Grate    Stokers 95 

Chemical  Action  on  Hydrocarbons  in  Furnace 40 

Chemical    Reagents    16 

City  of  Chicago,  Department  of  Smoke  Inspection 60 

Clinker  Grinder 109 

Clinker  Grinder,    Exhaust   Steam   Under 110 

Coal  Magazine   for   Murphy   Furnace 107 

Coal  of  Low  Combustible,  Ignition  Arch  for 137 

CO,    Formation   of 41 

Coking  Arch 51 

Coking  Arch,  Function  of,  in  Combustion 51 

Coking  Arch,  Location    of    51 

Coking  Plate  for  Murphy  Furnace 107 

Combustible    in   Ash 7,  8 

Cumbustion  Arch    55-57 

Combustion  Space,   Definition  of 54 

Combustion  Space,  Size  of 54 

Conditions  for  Furnace  Efficiency  64 

Conditions  for  Setting    Blonck    M.eter 79 

Conditions  for  Smokeless    Combustion 46 

Conduction    65 

Connection  of  Blonck  Meter  to  Boiler 75 

Connection  between  Uptake  and- Breeching 143 

Construction  of  Blonck    Meter 75 

Construction  of  Chain-Grate  Stoker 91 

Construction  of  Clinker    Grinder    109 

Construction  of  Double    Sprung   Arch... Ill 

Construction  of  Wilsey   Gauge   68 

Control  of  Draft,  How  Best  Accomplished 25 

Convection    66 

Covering   for   Brickwork 23 


FURNACE   EFFICIENCY  151 

Cuprous  Chlorid  16 

Curved  Deflector  in  Breeching 144 

D 

Damper,  Effect  of  Position  on  Draft 25 

Damper  to  Prevent  Infiltration  of  Air 101 

Dead  Plate   in  Jones   Stoker 122 

Dead  Plate,  Purpose  of 122 

Deflecting  Arch 62-131 

Defective  Baffles.  Effect  of,  on  Draft  Losses 32 

Design  of  Breeching  140 

Design  of  Chain-Grate    Stoker    92 

Design  of  Furnace  for  High  Temperatures 48 

Design  of  Ignition  Arch  131 

Design  of  Links  for  Stoker 93 

Design  for   Smokeless    Combustion 55 

Diagram  of  Wilsey  Gauge 68 

Differential  Draft  Gauge.  Function  of 76 

Dilution  of  Furnace  Gases 22 

Dirty  Tubes.  Effect  of.  on  Draft  Losses 32 

Disc  Valves  for  Jones  Stoker 124 

Distillation  of  Gases  from  Coal 48 

Double-Arch  62 

Double-Arch   Bridge-Wall  Furnace 60 

Double  Sprung  Arch,  Construction  of Ill 

Double  Sprung  Arch   for   Murphy   Furnace 110 

Double  Sprung  Arch,    Support    for 110 

"Double-Web"   Chain-Grate   Stokers 95 

Draft,  Control  of.  with   Light  Load 29,  30 

Draft,  Determination  of  Proper 24 

Draft,  Effect  of  Too   Much 24 

Draft,  Effect  of  Too   Little 24 

Draft  for  Jones  Stoker 120 

Draft.  Function  of 23 

Draft  Gauge,  Cost  of 21 

Draft,  Loss  over  Bridge  Wall,  Meaning  of 31 

Draft,  over  Fire 37 

Draft  Pressure  Losses.   Causes  of 77 

Draft  Pressure  Loss    in    Breechings 141 

Draft,  Production  of 24 

Draft  Required  with  Horizontal  Baffles 55 

E 

Effect  of  Heat  on  Coal 40 

Efficiency  and   Capacity  60 

Efficiency  of  Heat  Transfer  66 

Efficiencv  of  Heat  Transfer,    Formula   for....  .  67 


152  FURNACE   EFFICIENCY 

Efficient  Furnace,   Definition   of 3 

Engineering  Experiment   Station 55 

Essential  Condition  for  Smokeless   Combustion  90 

Excess  Air,  Formula  for  5 

Excess  Air,  Further  Causes  24 

F 

Fans  for  Jones  Stoker  123 

Faulty  Boiler  Design,   Effect  of,  on  Draft  Losses 32 

Feed  Gate  for  Chain-Grate  Stoker 97 

Feeding    Coal   to    Murphy   Furnace 106 

Fire-Clay  Tile  60 

Fire-Tube  Boilers  60 

Flat  Arch,   Radiation  from 133 

Flat  Ignition  Arch  58-98 

Flue  Gas  Apparatus,  Cost  of 21 

Flue  Gas,  Obtaining  Sample  of 17 

Flue  Gases,  Heat  Carried  Away  by 6 

Flue  Gases,  Temperature  of  - 6 

Flue  Gas  Tests  to  Determine  Efficiency 22 

Formula  for  Height  of  Smoke  Stack 146 

Free-Burning  Coal,  Ignition  Arch  for 136 

Free-Carbon  in  Smoke,  Amount  of 41 

Fuel  Economy  Gauge  65 

Fuel  Economy  Gauge,  Design  and  Construction  of 66 

Function  of  Boiler     2 

Function  of  Boiler    Furnace    .- 2 

Function  of  Clinker   Grinder   109 

Function  of  Deflecting  Arch   62-131 

Function  of  Ignition   Arch   58-131 

Function  of  Sprung    Arch    58 

Function  of  Stoker   Boxes   108 

Function  of  Water-Back   100 

Furnace  Gases,  Velocity  of,  over  Bridge-Wall 31 

Furnace  Gases,  Volume  of  31 

G 

Galvanometer 68 

Grate  Bar,  Construction  of  in  Murphy  Furnace 106 

Grate  Bearers  for  Murhpy  Furnace. 109 

Grate  Bearers,  Support  for 109 

Green  Chain-Grate    Stoker    55-93 

Green  L.  Type  Stoker 101 

Green  Stoker,   L.   Type 101 

H 

Hand  Firing  48 

Hay's  Flue  Gas  Apparatus... 17 


FURNACE   EFFICIENCY  153 

Heat  Distribution   for   Illinois   Coal 42 

Heat  in   Furnace   Gases 66 

Heat  Liberated  from  Furnace 66 

Heat  Lost  in  Smoke   Stack 66 

Height  of  Smoke  Stack,  Formula  for 146 

Heine    Boiler  55 

Heine  Boiler,  Direction  of  Gas  Flow  through 34 

Heine  Boiler,  Draft    Losses    through 34 

Holes  in  Fire,  Loss  Due  to 7 

Horizontal  and  Vertical  Baffles  as  Regards  Smoke 55 

Hydrocarbons    40 

I 

Ignition  Arch    131 

Ignition  Arch,  Action  of  132 

Ignition  Arch,  Construction  of  99 

Ignition  Arch,  Design    of 131 

Ignition  Arch  for  Coal  of   Low  Combustible 137 

Ignition  Arch  for  Free-Burning    Coal 136 

Ignition  Arch  for  Texas    Coal 137 

Ignition  Arch,  Intensity   of    Radiation    from 133 

Ignition  Arch,  Length  of 138 

Ignition  of  Entering  Fuel 98 

Incomplete  Combustion,  Effects  of 41 

Infiltration    of   Air ICO 

Intensity  of  Radiation  from  Ignition  Arch 133 

J 

Jones  Stoker,  Automatic    Features    of 123 

Jones  Stoker,  Dead   Plate   in 122 

Jones  Stoker,  Disc   Valve   for 124 

Jones  Stoker,  Draft  for 120 

Jones  Stoker.  Fan   for 123 

Jones  Stoker,  Operation   of 126 

Jones  Stoker,  Points   of  Superiority 128 

Jones  Stoker,  Ram   Case   for 121 

Jones  Stoker,  Rate  of  Fuel  Feed  to 123 

Jones  Stoker,  Removal  of  Ashes  from 127 

Jones  Stoker,  Tuyer    Blocks    for 121 

Jones  Under-Feed  Mechanical   Stoker 119 

L 

Length  of  Ignition  Arch 138 

Links  for  Stoker   Chain „ 94 

Links  for  Stoker,   Design   of 93 

Location  of  Water-Back   100 

Location  of  Wilsey  Gauge  on  Boiler 70 

Long  Ignition  Arch,  Action  of 135 


154  FURNiACE   EFFICIENCY 

Loss  of  Heat  when  CO.  is   Formed 41 

Lo..wer    Gauge 78 

L.  Type  Stoker,  Action  of....  ..  101 

M 

Maintaining  Furnace   Conditions 65 

Material    of    Breechings 142 

Mechanical  Stoker   48 

Mechanical  Stoking,  Under-Feed  Principle 119 

Method  of  Driving  Cha:n-Grate  Stokers 96 

Motion   of  Stoker  Boxes 108 

Murphy  Furnace     106 

Murphy  Furnace,   Coal  Magazine  for 107 

Murphy  Furnace,  Coking    Plate    for 107 

Murphy  Furnace,  Construction    of , 106 

Murphy  Furnace,  Double  Sprung  Arch  for 110 

Murphy  Furnace,  Feeding  Coal  to 106,   107 

Murphy  Furnace,  Grate    Bearers    for 109 

Murphy  Furnace,  Motion  of  Bars 106 

Murphy  Furnace,  Operation  of 112,113 

Murphy  Furnace,  Stoker   Boxes   for 108 

N 
Normal  Draft  Conditions,  Importance  of 37 

O 

Observation  of  Smoke 43 

Operation  of  Jones   Stoker 126 

Operation  of  'Murphy   Furnace   112 

Operation  of  Wilsey   Gauge T 69 

Orsat  Apparatus,  Operation   of 13 

Orsat  Apparatus,  Reagents    for 12 

Orsat  Gas-Analysis   Apparatus   10 

P 

Path  of  Furnace    Gases 54-58 

Path  of  Gases 57 

Platinum    Coils 68 

Points  of  Superiority  of  Jones  Stoker ..  128 

Poorly  Designed  Furnace  as  Cause  of  Smoke 48 

Potassium   Pyrogallate 16 

Pressure   Water-Back   

Prevention   of   Smoke 46 

Principle  of  Blonck   Meter  

Principle  of  Fuel   Economy   Gauge 66 

Principle  of  Progressive   Combustion  90 

Problem  of  High  Efficiency 64 

Progressive    Combustion 90 


FURNACE  EFFICIENCY  155 

Proper  Draft,  How  Determined 25 

Proper  Heights  of  Smoke  Stack 146 

Purpose  of  Ram  for  Jones  Stoker- 

Pyrometer  66 

R 

Radiation  66 

Radiation   from    Flat   Arch 133 

Ram  Case  for  Jones  Stoker 

Ram  for  Jones  Stoker,  Purpose  of 121 

Rate  of  Combustion  as  Affected  by  Furnace  Draft 37 

Rate  of  Fuel  Feed  to  Jones  Stoker 123 

Ratio  of  Furnace  Draft  to  Uptake  Draft 36 

Reason    for    Smoking 51.  54 

Red  Gauge  in  Blonck  Meter 75 

Relation  of  Draft  Losses  for  Good  Economy 30 

Removal-  of  Ashes  from  Jones  Stoker 127 

Removal  of  Broken  Links  in  Chain-Grate  Stoker 93 

Return  Tubular  Boiler,  Draft  Losses  through 29 

Ringleman   Chart 

Ringleman  Chart,  Construction  of 43 

Ringleman,  Chart,  Use    of 43 

S 

Sampling  Pipe  17 

Sampling  Pipe,  Air 

Sectional  Area  of  Smoke  Stack 146 

Setting    Blonck    Meter 75 

Short-Circuits    through    Baffles 34 

"Side-Feed"  Principle  in  Mechanical  Stoking ..  106 

Single   Arch 62 

Smoke  -'- 40 

Smoke  as   Index  to  Furnace   Conditions 41 

Smoke  Densities,  Designation   of 46 

Smoke,   Formation   of 41 

Smokeless  Combustion  58 

Smokeless  Combustion  with   Fire-Tube   Boilers 60 

Smokeless  Furnaces.    Design    of 51 

Smoke,  Objections  to 

Smoke  Record  46 

Smoke  Stack    146 

Smoke  Stack,  Proper    Heights    of 146 

Smoke  Stack.  Sectional   Area   of 146 

Smoke  Stack.  Velocity  of  Gases  in 146 

Sprockets  for  Carrying  Chain 96 

Sprung  Arch 57 

Sprung  Ignition   Arch 134 


15G  FURNACE   EFFICIENCY 

Stirling  Boiler,  Draft  Losses  through 36 

Stoker  Boxes,  Function   of 108 

Stoker  Boxes,  Motion    of 108 

Stoker  Boxes  for  Murphy  Furnace 108 

Support  for  Double   Sprung  Arch 110 

Support  for  Grate-Bearers    .                                                    ..  109 

T 

Table  No.  1 42 

Table   No.  2 71 

Texas  Coal,   Ignition   Arch   for 137 

Thermometer,   Cost  of 21 

Thin  Fire,  Effect  of,  on  Draft  Losses 29 

Tile   Roof 54,57 

Torch  for  Locating  Air  Leaks 22 

Tube  Tiles 54 

Tuyer  Blocks  for  Jones  Stoker 121 

U 

Under-Feed  Principle  in   Mechanical  Stoking- 119 

Upper  Gauge 78 

V 

Value  of  Wilsey  Gauge 72 

Velocity  of  Gases  in   Smoke   Stack 146 

Velocity  of  Gas  in   Breedings 141 

Volatile  Gases,   Composition   of 40 

Volatile  Gases   in   Coal 40 

W 

Water-Back    99 

Water-Back,  Function   of 100 

Water-Back,  Location    of 100 

Western   Society   of   Engineers 57 

Wheatstone    Bridge 68 

Whitewash  for  Stopping  Air  Leaks 

Wilsey  Fuel   Economy  Gauge 65 

Wilsey  Recording  Gauge  72 

Wing   Walls 48 


One  Thousand  Questions  and 

Answers  for  Engineers,  Applicants 
for  License  and  Electricians 

By  JOSEPH  G.   BRANCH,   former  Member  of   the 

Board    of    Examining    Engineers    of    the 

City   of  St.   Louis,   Editor  "Practical 

Electricity  and  Engineering." 

This  book  contains  questions  with  answers, 
asked  by  Examining  Boards  for'engineer's  license, 
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The  book  is  printed  in  large  type,  fully  il- 
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The  Electric  Motor 

and   Its  Practical  Operation 

By   ELMER    E.   BURXS 

The  only  book  giving  a  simple,  clear  and 
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Chapter  1. — How  an  Electric  Current  Can 
Produce  Motion. 

Chapter  II. — The  Beginning  and  Growth  of 
the  Electric  Motor. 

Chapter  III. — Power  and  Efficiency  of  a  Motor. 

Chapter    IV. — Counter-electromotive    force. 

Chapter  V. — How  Power  is  Lost  in  a  Motor. 

Chapter  VI. — Armatures  and  Cummutators. 

Chapter  VII. — Types  of  Direct-current  Motors. 

Chapter  VIII. — Starting  Boxes  and  Their  Connections 

Chapter    IX. — Curve    Tracing. 

Chapter  X. — How  to   Understand  Alternating-current   Motors 

Chapter    XI. — Operation    of    Alternating   Current   Motors 

Chapter    XII. — Speed    Control   of    Motors. 

Chapter   XIII. — Motor   Troubles   and    How    to  Cure  Them 

Chapter  XIV. — Selecting  and  Installing  Motors 

Appendix.— Horse-power    Required    to    Drive  Various  Machines. 

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Steam  Publications 

STATIONARY  ENGINEERING 

By  JOSEPH  G.  BRANCH,  B.  S.,  M.  E. 

Former  Chief  of  the  Department  of  Inspection  Boilers  and  Eleva- 
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chanical Engineers,  Etc. 


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Practical  Mathematics 

FOR  THE 

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By  ELMER  E.  BURNS  and  JOSEPH  G.  BRANCH. 


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ten especially  for  the 
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illustrations  h  a  v  e 
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CONTENTS 

1.  Common  fractions. 

2.  Decimal  fractions. 

3.  Use   of   decimal    fractions    in    finding   circumference    and 
area  of  a  circle. 

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5.  Reducing  common  fractions  to  decimals  and  decimals   to 
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6.  Finding  the  horse-power  of  an  engine. 

7.  Finding  the  capacity  of  tanks  and  boilers. 

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9.  ALGEBRA.     The  use  of  letters  to  represent  numbers. 

10.  Addition  and  subtraction  of  algebraic  numbers  and  solving 
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Practical  Kinks,  Recipes 
and  Tables 

By  JOSEPH  G.  BRANCH,  B.  S.,  M.  E. 

This  book  has  been 
compiled  especially  for 
engineers,  electricians 
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inal and  useful. 

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containing  the  following 
recipes  and  tables : 

Pressure  of  Water. 
Standard  Steam,  Gas  and 
Water  Pipe,  with  usual 
prices.  Edison  Three- 
wire  System.  Caloric 
Power,  Carbon  Value 
and  Evaporative  Power 
of  Various  Fuels.  Met- 
ric Units.  Cost  of  Fuel 
Oils  as  Compared  with 
Other  Fuels.  Circumfer- 
ences and  Areas  of  Cir- 
cles. Weights  of  Iron 
Stacks,  with  Gauges  and 
Prices.  Air  Compressors 
—  Steam-driven.  Range 
of  Injectors.  Total 
Stored  Energy  of  Steam  Boilers.  Safety  Valves.  Ice  Tank  Pull- 
ing Record.  Electric  Wiring  Table  for  Daily  Use.  Coal  Capac- 
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Engine  Speeds  for  a  Frequency  of  Fifty  Cycles  per  Second. 
Melting  Points  or  Temperatures  of  Fusion.  Resistance  of  Cop- 
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Different  Kinds  of  Kiln-dried  Woods,  and  Their  Evaporative 
Power,  Compared  with  Coal  of  Average  Quality.  Circumference 
of  Circles.  Wiring  Tables  for  Electric-light  Conductors.  Com- 
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